560 SEL Rough Idle (Another one!)
 

OK. I really need help now. I don't want to take this thing into the shop to have this diagnosed, but I still have a rough idle problem on my 560 SEL. It's rougher when cold, and gets better when warm, but still feels like a cylinder is "missing" occasionally, even though no bad cylinder can be isoloated by pulling the plug wires.

So here are the exact symptoms:

Oil pressure gauge fluctuates with the roughness, though the change in RPM is not sensitive enough to be seen in the tachometer. The roughness feels like the engine is being hit with something occasionally.

It seems the engine is reving and slowing down in 5-second cycles, though it is too subtle to see on the tachometer. It can be heard, though, when under the hood.

It's driving me nuts!

Here are some background facts:

1. Vacuum is great - tested it with a gauge, and visually examined everything.

2. New injectors, seals, seats, etc.

3. New fuel filter

4. All secondary ignition parts new (wires, plugs, coil, cap, rotor)

5. Air filters new.

6. OVP valve new

7. Fuel pump relay new ('2000)

8. One of the fuel pumps looks new.

9. 98 k miles

10. All parts OEM.

Any way I can diagnose this without going to the dealer?

Thanks for any help....

Correction
 

By "OVP valve" I mean OVP relay...

Well, I don't know if you've checked this but have you considered your cold start valve? My 560 didn't need it, but when I got her I decided that I'd replace every valve, vac line, and all of the little odds and ends under the hood to get a squeaky clean look whether the part was working fine or not (I'd just put the old part in the new box and file it on my "560" part shelf;)

This was my first 126 (as I'm a 115 fan) and I would do a little research on the 126 parts as I replaced them... the cold start valve is one of the components that helps with the immediate startup and idle of the car when its cold... You may also want to check out your o2 sensor although usually it would run a bit rough after warmup because that's when the o2 really kicks in when hot and sends the info to your computer for it to tell your electronic fuel components what to do as far as the correct mixture,etc.

Mine was surging, and getting some crappy gas mileage as well as a rough idle once the car got up to operating temp.I could also smell a sulfur-like odor sometimes when at idle and noticed that my o2 sensor light went off a couple of times and although it didn't stay on, I figured it was either GOING to go or is gone. I replaced it and she's running fine cold or hot. How's the ride when you're on the accelerator (on the highway)? Does it also surge or use more gas than usual? Sometimes it may be sluggish when you hit the accelerator although the tach will show you using a crap load of gas to get going. Hope this helps.

also try a search on rough idle or similar and see if that will give you some ideas. Good luck!

Alan

Had the same thing on my 88 560sel - did all your stuff same thing. What worked for me was replacing the fuel lines. They were so rusted inside that one broke in two from it's own weight when we removed it. The rust is not trapped in the fuel filter as the filter is in the back of the car and the fuel picks up the rust and takes it to the fuel distributor. Take the injector lines off the fuel distributor and carefully pull out the screen in each injector line hole. I think you will find them partially clogged with dirt. I cleaned my screens and replaced them - you can put new ones in - but check your fuel lines first. Before i changed my fuel lines - I cleaned the screens and the car idled perfectly for about 100 miles and started to act up again. Try cleaning or replacing your screens - they are cheap from Phil and if the problem goes away - then you know to change your fuel lines. The oil guage on mine fluctuated the same way - the tach barely showed the missing but you sure could hear it and feel it - it was annoying. Hope this helps you.
Just had a crazy thought - if you do have rust in your lines and want a cheap fix (I didn't think of this until now!) cut the fuel line in two just before it goes into the fuel distributor and cut off about 3" of line and put in an aftermarket - cheap inline fuel filter with rubber hoses. Clean your screens and that should work . If you get one of the see through fuel filters you should be able to see the rust in it after you drive for a while. Surprised Mercedes didn't use one up front for contaminants from the long fuel lines.

Thanks for the replies
 

DJNEWK2 - I'll try your approach when all else fails. I thought that a bad cold start injector could be part of the problem. But so could be the idle control valve, the fuel pressure regulator, the old fuel pump in the back, the ignition control module, the idle control module, the fuel ditributor, and the O2 sensor (though taht's less likely, since the idle improves significantly as the car warms up, and the emissions are good) . I.e. I'd rather diagnose first at this stage rather than use new parts as a process of elimination. Eventually I might have to do what you suggest, however.

moedip - I've heard of the clogged screen problem before, and I am very eager to explore this. Since now I am dealing with a very costly part (the fuel distributor), I'd love to know how you got the screens out (would dental picks work?). Also, exactly what fuel line did you replace? The entire line from under the car?

The idea of installing a clear aftermarket in-line fuel filter strikes me as particularily smart. An added safeguard plus a diagnostic tool.

An old German mechanic gave me the tip for removing the screens - get a long thin very sharp screw and gently turn it into the screen just so it grabs and lift the screen out. the sharp point will not leave a big enough hole to cause problems. Yes I replaced the two fuel lines (feed and return) They were a pig to get out and in around the rear axle area by the gas tank - but 4 hours and a little cussing and a couple of beers later it was done. It really helps if you can get the car on a hoist to manouver the lines when replacing - we didn't have one and just jacked up the the driver's side as high as we could. When we picked up the feed line from one end to take it to the bench to inspect - it broke in half from it's own weight - it was so rusted. If you are worried about making too big a hole in the screens - order a set from Phil and keep them as standbys - they are cheap. I'm kicking myself for not thinking of the fuel filter idea until now!!!:mad: :mad:

moedip - I just talked to Phil
 

moedip - I just talked to Phil about those screens. He did not know anything about them, and wondered where you meant they could be found. I'd rather order them first before I start futzing with this, because I want to know what the part looks like before I try to extract it...

On your fuel distributor there are 8 metal lines that go to your injectors. When you remove the metal lines from the distributor - they were inside the hole you took the metal line off of, at least they were in mine.

moedip - Yup, that's what I thought. I tried getting one of these screens out when I did my injectors (I removed the injector lines for the job). Used a wood screw. I guess it was not thin enough, because it grabbed the side of the wall, and I did not want to ruin anything on the distributor, so I stopped. I'll try it again.

I bought some dental picks the other day - one of them looks like it would be perfect for the job - sharp point, yet a small curve at the end, so it could grab below the screen.

Whish these things could be ordered as spares. Does not seem so, unfortunately.:(

I think you are most likely correct about this being the problem. I can't wait to go in there again this afternoon and checking for those screens...

When in doubt - improvise!
1) I cannot believe that they are not available - how about right from Mercedes?
2) If a fuel filter is put in just before the distributor -and the screens are not available- can they be eliminated with the added protection of the filter?
3)If Mercedes doesn't have them - can a similar screen be used from another car manufacturer?
Just a few ideas to do work arounds. It seems like I have to do work arounds a lot lately.

moedip -

Did not get around to it today - will look at those screens late tomorrow afternoon. Somehow I think this is it. I've read about the same problem with the same symptoms on another site. I'll keep the thread informed...

If the idle is fluctuating up and down, perhaps your fuel mixture should be adjusted. As far as the rough idle, that might take care of it. If not, when the engine is running and the aircleaner off, get a 12mm wrench and one by one, loosen each fuel line in the fuel distributer, see if the idle gets worse or doesnt change, then retighten. If you come across one where it doesnt affect the idle, then its that cylinder that is causing the problems. This is how my mechanic diagnosed my rough idle (worse when cold) on my 420. Turns out I have a bad exhaust valve in the no. 8 cylinder and is not sealing properly. For the money to fix it, I will live with the rough idle ;)

amg280 - I tried a cylinder isolation approach by disconnecting the spark plug cable cylinder by cylinder. I could not isolate a bad cylinder.

The mixture is something I'll look into. The problem there is that this is not DIY - you need something to read your exhaust emissions for this. Before I take it to the shop, I'd like to narrow it down. I'd hate to take it in, have a mechanic do the mixture, it not work, he tears the whole thing down and tells me it need a new fuel distributor, when all I really needed to do was clean the screens and replace a fuel line.

I wish I had my own shop, lifts, scopes, everything...:o

Don't think fuel mixture will help. I paid Mercedes to do mine with absolutely no change. As I said previously I did all the things you did with no change. For others please note- the miss is not rythymic it is a a constant random type of miss - not like one cylinder missing - sort of hard to explain until you see it. Pick up, mileage and power are great the only thing is the slight missing at random at idle - everything else is good.It's not really bad- just enough to get your attention. The main thing that gets your attention is the oil guage fluctuating in time to the miss and the SOUND of the motor changing in revs at idle. When a Flagship like a 560sel has a slight miss it really bugs you! :p

Could not have said it better (or described it better), moedip!

This afternoon I'm going to look for those screens...

moedip - Turns out there are no screens inside the fuel destributor on my '89 560 SEL. Just went and checked - nothing. Maybe they changed them in '89, which would explain why Phil coud not find them.

I'm back to square one. I had really hoped that this would take me closer. I am beginning to worry its something more fundamental, like a stretched/worn chain or bad valves. Somehow I think my fuel lines are fine.

If it was a bad valve, it would show up when you islolated each cylinder. Its unlikely that more than one went bad at once. Look at your vacuum lines real good with the air cleaner off. There is one in particular, near the intake, that is like a U shaped. This one is known for coming off, and it will make a rough idle and will make ur exhaust note seem like a muscle car at idle.

Im not sure at what it does but its worth looking at, even though im sure you probably did this already. Other than that, it may be a bad fuel distributer. Had one on mine, after weeks of trying to find the culprit. They are somewhat hard to diagnose. If you have any new developments let me know, Id be interested in hearing them. I feel your pain, trying to diagnose a bad idle on a mercedes is a difficult and expensive experience, as it is discouraging.


Gook luck!

-Andy

Andy -

How about a bad cold start injector? The idle is rougher when cold, then cleans up as the engine warms up, though it's still a touch rough then (as described in the beginning of this thread). If it's bad and leaky, it could still be making the fuel mixture too rich randomly as it shoots fuel into the manifold after the engine heated up. Does that scenario make any sense?

Henry - Since you have no screens - I'd still put a fuel filter in the line by the distributor to catch any contaminants from the fuel line - good insurance if there is rust that will also protect your fuel distributor. My car sat for four years before I got it - water could have been sitting in the lines to cause my problem. Was your car sitting for a long time? In trying to solve my problem - my change list included: both fuel pumps, fuel filter, accumulator, idle valve clean, new distributor cap and rotor, new wires, new plugs - make sure you use copper NOT platinum plugs - as they can cause rough running, vacuum lines checked for leaks, compression test, air pump replaced, egr valve changed and I can't remember what else! I had the timing chain changed on mine with no difference. I took it to Mercedes for a diagnostic and got a clean bill of health. Still had the miss - until the lines were changed.The only other thing - if it acts worse cold - is the idle valve - have you taken it out and cleaned it real good with brake cleaner? If not clean it with brake cleaner until there is no more crud coming out - make sure the piston moves freely - then spray the inside with a coating of spray silicone and let sit for an hour for silicone to dry then reinstall. Before I cleaned my idle valve - the car had a buzzing sound from the engine when it was left sitting for a month and then started - as the engine warmed up it went away - cleaning the valve stopped that.I know your injectors are new - but if you have a little dirt from the fuel line getting through to them - they may need to be cleaned. I'd put the fuel filter into the fuel line by the distributor and pour Techron or other strong injector cleaner into the tank and drive it looking for an improvement in a few hundred miles.Keep me posted - I REALLY do feel your pain and will try to help.:( :(

moedip -
So you just went to an auto supply store, got any old in-line fuel filter, cut the rubber part of the supply line, and just inserted the filter with some hose clamps? Sounds like a 10 minute job. And this won't reduce fuel pressure or bring anything out of spec? Could be an effort well spent.

I am still curious if a bad cold start injector could have anything to do with this. Also, since cleaning the idle air valve does not take buying any parts, that could also be an effort well spent. You said spray it with silicone - do you mean a silicone lubricant, such as silicone door spray?

One thing I noticed is when the engine is cold, the idle speed fluctuates (I described this earlier), then settles down as it heats up. I can clearly hear a "clack-clack-clack" sound coming out of the front of the valve train in cycles - it comes and goes with. This sound continues in cycles even as the idle speed settles. Which is why I suspect a bad chain (It takes 8 revolutions of the chain to go through, so if a bad area of the chain passes It could be throwing the timing off, confusing all that lovely digital technology.) That's why I fear the whole thing may be out of whack.

It has plenty of power, it's only the idle stuff that drives me nuts!

Yeh - the clear silicone spray you would put on doors and rubber.I just used it as a dry lubricant for the piston. For the clacking sound - 2 things - how many miles on the car? Timing chains are usually good for 200,000 miles - the plastic chain guides and tensioner are the real problems to look for on this and the 420 engine. They should be done every 100,000 miles for peace of mind. The plastic guides and tensioner are cheap and if you do a search on this site Mike Tangas posted a real good article with step by step instructions on changing them. I think my tensioner and guides came to about $70. I changed my chain at about 160,000 miles and found I didn't have to - there was no stretch in it at all - when I held it by one end and lifted it it had the same amount of sag as the new chain. I don't think the clacking is chain though - more likely lifter sticking. Is it always there? always the same cycling? or does it clack in cycles and disappear and come back again randomly? I only drive my 560 occasionally for fun - not daily - if it sat for a month or so and I ran it - I had a little clacking sound on the passenger side bank from a lifter that went away after a 2 hour cruise. I used a can of Wynn's upper cylinder lubricant in the oil (says it quiets noisy lifters) and it slowly went away. - For a couple of bucks worth a try. If the noise stays there afterwards - then suspect chain or guides. From what I have read -normally chains make noise when cold and just starting up and tends to get less as the engine warms.Mike's article tells you what to look for on the plastic guides before changing - if I remember right - if they are the color of beer bottles - change them - new ones are white.
As for the filter - how can it change the fuel pressure? Once it is in the line nothing else is different. One suggestion though - I don't know the fuel pressure on this car - just check and make sure the new filter will operate at the pressures of this system whith the supply store you buy it from and you should be home free.

moedip - I really appreciate your advice.

the clacking sound goes in cycles - comes and goes. Warm or cold.

This car has 98k miles....

I've been reading Mike Tangas's adventures of rescuing a 560 from the junkyard. Quite amazing.

You think I'd be able to find an appropriate filter at TrakAuto?

One thing I know is if you've got one problem, you can usually get to it deductively. If you have two, you'll go crazy. My next steps will be:

1. check the wires at the idle control unit
2. install a clear fuel filter (also to monitor condition of the fuel line)
2. clean the idle air valve as you described

Any way I can test the cold start injector? In one post on this site a person pulled it, left it attached on the side, and then plugged the hole (of course with the car completely warmed up), and then started the engine.

Don't know on this car but on Vw gas jobs we pull the fifth (cold start) injector out of the manifold and crank the engine with the high voltage lead to the distributor removed with the engine warm and aim the injector into a glass jar and watch for leaking. With the electronics on this car I would be hesitant to do that as I have learned from experience that the spark generated can reach 1 1/2" in length (Mercedes always seems to overdo it!)So I would agree with plugging the manifold hole and seeing if the injector is leaking with the engine warm. If the injector was not supplying fuel - the car would have starting problems -which is not the case - so a cold check is not required.
Was you car sitting for a few years in the past?
I would go with your 1-3 ideas first and put in stong injector cleaner in your tank or that $20 stuff in a metal can by Duralube or others called fuel system cleaner and conditioner - That stuff is what I used when I got about 100 miles with no missing - now that I remember (Bear with me at times - as I get older I forget somethings until my memory gets tweaked!) and drive for a while. If there is any dirt in your fuel distributor - it will also clean it as well as your injectors. I have learned a long time ago -sometimes the solution is very simple - but you get too complicated and miss the simple things.
Check this site for what the fuel pressure is coming from the accumulator and ask the guy at the counter if the filter will work at that pressure.
I just finished putting in a rebuilt engine and tranny in my son's car and will be finishing it off this weekend - bet I know where you will be!!!:D :D :D

On the drivers side inner fender wall, down above the AC receiver drier, there is an ignition control unit. It has a vacuum line going to it. MAke sure that line is still there. It will be near the ABS motor. Worth a shot, since we are covering every avenue. I know it will idle weird with that hose detached.

As for the cold start valve, hmm, honestly not sure, but If it still does it when warm, maybe not. Another thing I was thinking of, since you said the engine flucuates...is a bad intake gasket.

Since you said the idle gets better when warm, maybe the engine expands, and thus sealing most of the leak, which would explain why it idles rough when cold. Although I never seen one go bad on these cars before. Oh well, worth a shot. Try spraying some carb cleaner around the intake when its cold and idling funky. If the idle jumps, you have a leak.

Keep me informed,

-Andy

moedip - I could not find a clear gas filter that would be up to spec with the fuel pressure. I checked several stores - one flatly said they're not aware of any clear ones that are up to spec. Which one did you put in yours?

Andy - I checked that vacuum line - it's connected. Bought some carb cleaner to check for other vac leaks and try out your theory of a bad intake gasket.

On a speperate note and off - topic, I can't find any of the approved oils (basivcally avaiation hydraulic fluids) for lubricating the throttle linkage. Has anyone substituted any of these, or know where to get them in the states (or where to order some on the web)?

Hi Henry - If you read my post - I JUST thought of it - putting the filter in - I didn't put one in mine as I changed the fuel lines. Even if you can't see though a metal one - it will still filter out any dirt from your lines. Then, once in, if you use the fuel system cleaner in your gas tank and drive a couple of hundred miles - it will clean out your fuel delivery system and anything cleaned prior to the fuel distributor will be trapped by the new filter and the filter in the back of the car. Also any dirt in your injectors will be cleaned by this stuff and you should be OK. Very inexpensive to try compared to some of the things you can do and might solve your problem. Also -has you car been sitting for a long time(year or two or three) or has it been in continuous use for years. You must remember that at higher engine revs minor things will not show up as much as the more critical levels for a maintained slow speed idle. As I said before - don't start getting complicated until all SIMPLE things are tried. I do remember that when I put the fuel system cleaner stuff into the tank with my old lines - smoother idle did not occur until I had used about 1/2 a tank and after about 100 miles the missing returned. If you want a stonger solution for more cleaning power - add the stuff when you have about half a tank and drive it until near empty. The worst that could happen is nothing - the best is - the idle problem will be solved and with the added filter may not return - even if you leave the old lines in. What have you got to lose??

moedip -

Well, I did the first part of your recommendation at this point - cleaned out the idle air valve. It's drying right now. A ton of crud in it. Fairly easy job, though. Only takes a few mintues to pull it.

Next I will go (again!) and look for a fuel filter I can put in. Running cleaner through the system now.

I have no idea how long this car has been sitting. All I do know is that right after I bough the car I found a mouse nest on the left hand side of the air intake - nestled between the air cleaner cover and the intake manifold. No fried mice, however...:D

Mice don't build in a moving car! - You confirm my suspicions - the car sat for a long time - you probably DO have rust in your lines. Once you have the filter in - then run the car with cleaner - so any crud it breaks loose will be caught by the filter not the fuel distributor. Keep me posted.OH - make sure the piston in the idle valve moves freely before re-installing it.
thanks
Maurice

Maurice -

I don't know what happened, but the car is smooth as glass at this point, both warm and cold. Not even a hint of roughness when warmed up - symptoms are ALL gone. RPM's are a touch higher.

Here are all the things I did since I started this thread:

1. Checked all vac lines - nothing
2. Added oil additive to clean out valve train
3. Added injector cleaner to the fuel
4. Went to the idle control unit. Removed it. Sprayed the bottom contacts and the plug with Radio Shack TV tuner cleaner
5. Thoroughly cleaned out idle air valve with brake cleaner, and lubed it with silicone spray. It needed it.
6. Re-checked plug wires for the umpteenth time. Found one not 100% pushed in (oops!)

Well - live and learn. I know it could not have been in the plug wires originally, because the problem existed when I bought the car, and I then replaced the plugs and wires. But still, it COULD have been No. 6 above as a new cause. Again, as we say in IT, one problem - you'll figure it out, two problems - you'll go crazy.

Still, I am going to look for a fuel filter. Sounds like a good piece of preventative maintenance, and that fuel distributor is expensive.

Anyhow, this car runs like a true charm. You can hardly tell the engine is running.

Maurice - thanks for all your help. I don't think I would have tackled the idle air valve without you telling me how to do it, and it was a simple thing to do.

Another resolved issue on the mercedes shop forum!!!

You are welcome Henry! BUT -T-T-T-T -- don't rest easy yet! I was fooled on mine. Wait a week or two and I will bet my bottom dollar that it will start to miss again - in say about 100 - 200 miles. The injector cleaner cleaned the injectors and the idle is good - unless you replace the fuel lines or put in that second filter - the dirt will again build up in the injectors and you will be cursing - wondering what went wrong! If you put the filter in NOW and add a little more injector cleaner to the gas when you have the filter installed - then I will agree that you have the problem licked! Look at the bright side - It cost me over a $1000 dollars and two years of trying things to get rid of that gremlin! - You got it resolved in less than two weeks!!! CONGRATULATIONS!!!
Maurice
PS - by the way - I have a new gremlin on mine - thought I had it fixed but I don't. Last year I drove my car to my mechanic friend's house and shut it off and was talking to him beside the car when this big plume of white smoke came pouring out from under the hood. The smoke came from the rear of the passenger side of the engine. When we had the hood up - we saw oil was dripping onto the back of the exhaust manifold. Looked like a valve cover gasket leaking. Ordered a new valve cover gasket and put it in - only AFTER the engine reaches operating temperature does the smoking start again but not as bad and gets worse when you make a left hand turn. Just looked at it again last month - took the valve cover off and cleaned the sealing surface of the head - checked the valve cover for warping and replaced the gasket again - I wiped off the residual oil from the manifold and started the car up - when the rest of the oil had burned off I shut the engine off. I started it the next day and brought it to operating temperature - no leak! Success - NOT. Everytime I take a left turn the smell of burning oil permeates the inside of the car - straight driving - nothing. I looked at the rear of the valve cover and again it was wet with a little oil. Frustrated - I loosened the valve cover and pushed up towards the fuel distributor on it and pushed it towards the front of the car - then tightened it. Thinking that I would get a better seal at the rear. No Luck. Right now I am down to only one thing. The valve cover gasket that was on the car and worked for 2 years before the smoke and the replacement one my mechanic friend got me were aftermarket. I notice that on the sealing edge of the gasket that it flat and about 3/8" wide and near the outer edge there is a slight raised round bead on the gasket that looks like it squashes down as you tighten the valve cover to give an extra secure seal. I am trying to find out if the Mercedes orginal gasket has two raised beads - one near the outside and one near the inside which should give a better seal. When I get to the bottom of it I will let you know. When it happens - the white smoke scares the devil out of you! Keep an eye out for this one. The smiling faces are for the top part of this post - could not figure out how to put them there so they are here!! :D :D

Maurice - Nothing is as it seems. I just checked my car AGAIN. Here is something new I found.

1. Start car - runs a bit rough (A/C off, gear in P), around 650 rpms or so.
2. Put in gear. Rpms drop to 550 or so. Car runs smooth - perfect.
3. Turn on AC. Rpms don't change. Still smooth.
4. Turn off AC. Rpms don't change. Still smooth.
5. Put the gear back into P. rpms go to 1100 or so. Rough. They don't go back down until I put it back in gear. When I do, it's smooth again.

In the manual they attribute a high rpm usually to the air intake valve - the part I just futzed with. But would I then not also have a problem in gear? And why do the rpms stay in spec when the car is in P after starting, but go out of whack when I shift back into P after having been in grear? Could it be a bad switch somewhere?

On your car, the valve cover gasket - has the "C" modification been done to your heads? Mercedes came out with a set of instructions on how to modify the gasket surface of the heads afer they changed the material of the replacement valve cover gaskets. You need to deburr the heads around the area of the fuel injector seal holders. This is not in the CD ROM or manual - I found it on ALLDATADIY.com. It's a Benz technical service bulletin. Here is how the text reads:

As of May 1991 production, the above mentioned engines are
equipped with valve cover gaskets made from a new material.

In case of repair of engines prior to production phase-in, install only the modified valve cover gaskets. To avoid later leaks, the respective cylinder head must be reworked prior to installation of the gasket in engines 116.96/117.96. The procedure is described in this bulletin.

1. Remove install injection valves and insulating sleeves.
2. Close off bores (A) completely, e.g., with paper and carefully cover valve train as well as air flow sensor (Figure 1).
3. Remove any burrs surrounding injection valve bores (A) (i.e. using a hand grinder) (Figure 1).
4. Hone gasket joint face (arrows) with emory cloth/sand paper (100 - 180 grit) or oil stone to remove any shavings, especially in the area around the bores (A, Figure 1).
5. Mark reworked cylinder head with the letter "C" (Figures 2 and 3).

There are a whole bunch of diagrams - I recommend you go look it up. I have not found the "C" on my heads yet, so I refuse to remove the valve cover gasket until I am ready to do this...

Henry - check the piston in the idle valve and make sure it is not sticking - if it is sticking it can cause the problem. Look into the bore of the valve with a bright light and see if there is any crud residual in the bore that could be causing the valve to hang up. Don't think you have a major problem here. Don't forget the sensors on this car cause different things to happen when engine is in park, drive, ac on - off etc - if the motion of the valve required by sensors does not happen idle will be affected. To see what I mean - pull the electrical connector off the idle valve and watch the revs pick up. OR - just drive the car for a few days and see if the valve frees itself up - if it worked once - it should again. In fact - after you put the filter in - I'd just drive the car for a few days and let the dust settle - then look at the idle at that time - easier and won't hurt anything!
This head mod you mention - the seal is good all the way around the valve cover except at the outer rear corner of the valve cover - the oil leak is very small - just a drop or two in a minute - but enough to cause smoke and smell - when I turn left the oil is pushed up against the outer part of the valve cover and the rear corner starts it's little drip - Do you think this mod around the injectors will cause the leak at the outer rear??
thanks

Maurice -

Don't know why it would leak there. Unless the leak is where they described the work should be done, and for some reason it travels along the side until it drips where you see it.

A valve cover leak should not be that hard to fix, unless something is bent (like the cover), or you have a marr on the head surface. Some manufacturers don't even provide you with a gasket - they expect you to simply create a silicone bead and then bolt the thing down over it. Maybe you should try a new cover gasket with a layer of silicone sealant?

Hi Henry - tell me about it - valve cover leaks are easy - right? I have just rebuilt a Vw Turbo Diesel and I maintain all my cars - but this stupid little gremlin is driving me nuts. The only thing I can see is that the valve cover just covers the head to the edge - there is no piece of head extending past the valve cover gasket. The rubber valve cover gasket pushes onto the bottom of the valve cover and goes up the side of the cover by about 1/2" both inside and out for a good seal. The sealing surface of the gasket is flat and about 3/8" wide. On the aftermarket one there is a round rubber bead about the height of a pencil lead molded into the bottom face of the gasket and about 1/16" in from the outer edge. If this bead is not grabbing the back of the head - I believe that is causing the drip. That is why I am trying to find out if a Mercedes gasket has another molded bead 1/16" from the INSIDE of the bottom of the gasket - as if it did - it would definately seal for sure. Like I said - a stupid problem. I don't want to use silicone unless it is absolutely necessary. The car was designed to work without silcone on the valve cover gasket - and by gum - it WILL work without silicone - or I will die trying!! The problem of being a purist!!!:D

I know the purist problem. I'd also use silicone only as a last resort.

On my idle problem earlier - Actually the fact that the symptoms are changing means I am getting closer and closer to the real cause. For example, the fact that it is now rough when in Park, AC off, warmed up (same missing sound as before), regardless of RPMs, and smoothes out when I am in drive, rules out a bad fuel supply (we'd be even rougher at the lower rpms, but it's perfect there). The idle air valve should not be affecting this. However, a dirty idle air valve could have skewed the entire system enough to mask the underlying causes. I think in my case it was a number of problems, and they are not all resolved yet. But I feel more and more certain it could be a bad throttle idle actuator switch (there is a technical service bulletin out - it causes irratic idle rpms) or actually a bad transmission/reverse light switch. The latter seems to make the most sense - I sometimes get a strange hesitation when I restart the car and put it into gear, only when warm, only occasionally, and only for a split second. The tranny engages right away, but the engine seems to lose power for a second or two. I interpret that as the engine having a slow time realizing it's in drive.

The fun thing is now I am begining to narrow it down, and the diagrams are beginnig to be of use....

Now you have hit something I didn't know about. - Where is this throttle actuator switch???
Thanks - I will change mine on principle.
Maurice

Maurice -

Sorry - I did not use the right name - it's the idle contact of the throttle valve switch. In the manual diagram it would be S29/2. However, the TSB only refers to the 1986 model.

Anyhow, since mine is not rough right now when I am at a red light, I'll wait a bit before I tackle this. Who knows - maybe it'll settle down.

Maurice,

Got ahold of a fuel filter that looks just right today. Cost a whole $3.75 US. This afternoon I'll depressurize the line, use my trusty garden pruners to just cut the rubber line in half, and put on the filter. Wish it were glass so I could see what's going on inside, but oh well....

This weekend I am taking the car on a 600-mile trip. This should give the cleaners I put in the fuel and the oil a good workout...

Hi Henry - at the end of your journey I will wager that your problem will be gone! Just wish I had thought of the filter before I changed my fuel lines - would have been a lot cheaper and a lot less hassle!! By the way - on a different topic - how are your door handles? Light faded gray that makes your car look old? Don't Laugh at what I am going to tell you - my wife did -but it works!! I read on this site last year that guys were putting peanut butter on their handles and rubbing it in and letting it sit awhile before rubbing it off and it brought the handles back to the nice dark gray they should be. Well - with my wife laughing her head off - I smeared peanut butter on my handles. Let me tell you - it has been 2 months and they still look new!!! Sometimes the stupidest simplist things work best! If you do it - do it in private or be prepared to be the butt of many jokes:D :D :D

Maurice - do I sense a hint of Candian mischieviousness??? :D :D :D


Actually - my look new and grey. But I did not use peanut butter.

I used a black trim restorer. Also works on tires. Really works.

Maybe it's made of peanut butter?:D

Henry - I swear - it really worked!!! I tried Armorall and other such products - but 2-3 weeks later they were dull again - laugh if you want - but it really did work!! When I want to be mischievious I go to an auto parts store and ask for a thermostat for a 1974 VW beetle (they are of course air cooled!!!):D :eek: :D :D

Maurice -

Ever noticed that the plastic bottles some peanut butter comes in get really waxy and sticky on the outside over time? It must have something to do with the peanut butter oil and its reaction with the plastic - the plastic must be absorbing it. Even happens when the peanut butter is in the refrigirator.

So I don't doubt it works. Maybe even just pure peanut oil works. Interesting....

Hey, we could manufactur a "patented compount" that restores all of your under the hood rubber, and really just be selling peanut buttern in an aerosol can! :p

We'd never get rich doing that - Let's patent the peanut butter and sell it as a mud pack to restore suppleness to skin!! Added bonus - you can snack as you pack!!!:D :D :D :D :D

Maurice -

The fuel filter is in. No leaks. Let's see how she holds up.

I think it was more preventative than anything, because I do think it could be more related to a switch or sensor at this point. Otherwise she'd be rough in "D" with the AC on - now she is only rough when warm and in "P" or "N".

I ordered the special diagnostic cable you can put on the various components, such as the idle air valve. It was US$ 28 something or another from Samstag Sales. I thought it might be a worthwhile investment for diagnosing components and working along the diagnostic flowchart using a multimeter. Being German and actually from the town the car was built in, I have this thing about following the book...

But all this can wait, because at least she now behaves when I'm at a red traffic light, and I am really beginning to enjoy the car.

I am now busy botteling peanut butter into spraycans....:D :D :D

Let me know how she runs after your trip this week end - Let's keep the fingers x'ed - BTW - will the spray cans be available in smooth and crunchy???;) :p

Hi Henry - wellllllll????????????

Did a great trip - went VERY smoothly (except for a screaming AC belt every once in a while when accelerating - gotta tighten that up!). No complaints except the occasional cruise control disengagement which I started a thread on on this board. Rough idle is definitely gone except when in Park and Neutral. Smooth as can be when in drive. Got about 17.1 mpg mixed (though mostly highway).

My weird "D" engagement problem I have complained about seems more and more like the dreaded B-2 piston, since it does not happen in "R". So next week I am taking it to the shop to have the transmission and tourque converter flushed, and the B-2 piston replaced (I don't have the time to do it myself), before it fails catastrophically on me. This guy offered me the use of all his lifting equipment in the shop if I decided to do the job myself. Nice! I have been a customer of his for six years.

These are great cars! I had it full of people. What a blast!

Before you go crazy on your cruise amp - I will tell you my little story. I did not use my cruise for about 2 years because I was working on various things on the car and did not take it on a highway run where cruise could be used. Last fall I took the car for a 40 mile run on the highway and engaged the cruise - the car started to slow down and speed up and sometimes felt like it wanted to stall with the cruise on - disengaging the cruise - the car was perfect - I then re-engaged the cruise and ran it with the speeding up and slowing down - as I drove - it seemed to get better - in the last 10 miles it never acted up once. I then had the car in winter storage from Oct. to May of this year. My first trip out - the cruise started to act up again - but after about 60 miles settled down and started to work perfectly. It has not acted up since. I am thinking that maybe contacts were dirty or corroded from sitting and by using it - they got cleaned off. Just my two cents worth! If you haven't been using your cruise for a while - keep using it regularly and see if it works better. If not - then check your amp. Cheers!!
Maurice

Maurice,

I've heard that before you suspect ANYTHING serious with the cruise you should clean & lube the throttle linkange. I already wanted to do that BEFORE this trip, so that's next on the agenda. Somehow I think it's something stupid and simple, like a bad contact or a loose switch, or the linkage being too stiff and therefor the actuator shutting out. Why? Because 90% of the time the thing works like a charm. It holds speed. All it does occassionally is disengage, usually abruptly during accelaration. Then, if you hit resume, it tries to find the correct speed, i.e. it will engage, and if it does not disengage again, the car will accelarate to the correct speed and hold, until I stop it or it disengages again. It could even be something dumb like a loose brake pedal switch or something like that.

I'm just happy as can be that I was able to trust this thing for a long road trip. Oh yeah - it turned 100k miles on the trip, and we took pictures of the odometer at 99999 and 100000! First time I've ever witnessed this!