idle on '88 560 SEL
 

We have an '88 560 SEL with an idle problem. the problem is that idles at 1300-1500 in neutral and feels like you are brake torquing in drive. In troubleshooting for a vacuum leak carb cleaner and wd-40 revealed nothing.
I disconnected a vacuum hose at the driver side front of the engine and connected a vacuum meter (22 in hg) and the went to less than 1000 in park and 650 in drive. I took it for a ride and it seems fine. I have capped both sides of the line and we are driving it. What have I done?
Searching through the enteries I see things about an idle speed control box and cleaning it, also something about an air screw on a 4.5. Do I have these and should I be cleaning and adjusting them. I tried to follow the throttle linkage around but found that it apparently goes everywhere!
Any help would be greatly appreciated.

All you have done is masked the problem. By taking off the vacuum line, you have lowered the timing and made the advance mechanism for the EZL ignition inoperational.

You most likely have a faulty idle air valve or something of that nature.

I would have to agree with benzmac.
Reconnect your vacuum. Then disconnect the electrical plug from your idle control valve if the rpm do not change that would definitely indicate a problem with the idle control valve. It is an easy fix, but expensive.

Thanks benzmac and mhingram(thanks for giving me a next step). I have reconnected the vacuum line to the EZL. I was able to locate the idle control valve utilizing the CD service manual. All these terms are new to me, I have done a lot on carbureted engines but haven't previously had trouble on my fuel injected vehicles. Anyway, on a cold start the idle is a little under 1000 and removing the connector makes a big difference. I then took it for a ride and the idle went up to 1200 and removing the connector again made a big difference. Is there a further test I can do on this valve?
In the area of the valve I noted that the big hose going toward the front driver side had been damaged and repaired. I didn't notice any change when I sprayed it with WD-40 and it looks like it is sealed but could it be a problem?
Finally, when this first happened I looked in the manual for things about idle and found an idle control unit that is supposed to be in the passenger compartment but couldn't find it. Should I continue my search for it?
Thanks,
Steve

Steve,
Sounds like your idle control valave is working okay at least it is acting like it is. I have a feeling that there is something else up for you. The normal idle for these beasts is 650 rpm +/- 50 rpm
whether in park or drive. So something is amiss. I believe it is probably an electronic sensor or a vacumm problem. The fact the idle is always high and not rough tells us that something is misreading the current idle speed or not adjusting it down. I am afraid I am not much help. Do you have a good shop that can scope the electrical side and gas emmission levels. Although this is probable only going to show a sympton of the problem. It might help narrow down the search
m

Actually the idle is rougher than I would like. I thied cleaning the idle valve, it was pretty dirty but no change. I thought I would go back to basics and check timing and error codes.
1. Are there codes and if so how do I read them? I can't find anything in the manual on it.
2. I found some specs on timing (3-7B no vac, 10-14 with) but can't find a procedure or where #1 is. When I used the driver front the reading was off the scale. I moved to what is #2 in most V-8's I was on the scale but moving the distributor had no effect. What gives?
Any help would be greatly appreciated!

#1 is clearly identified on the distributor cap (as are 2-8), provided you have an original Bosch or MB cap. Looking at the cap, #1 should be about 11 o'clock, give or take. #1 is also the cylinder closest to the radiator on the passenger side.

Timing is automatically adjusted through the EZL and crank sensor, so twisting the distributor will have only a momentary effect, then the EZL will readjust. Timing is not adjustable on your car. If you have twisted the distributor too far either way, you stand the chance of ruining a nearly indestructable cap. New from the dealer they cost $179.00. I just replaced mine as a Christmas present to the car, that and the fact mine was almost 17 years old (as speculated by the dealer due to the Bosch number rather than a MB #) AND I am going on a month long trip.

Such a length of service from a distributor cap makes up for the high cost.

steve, still trying to fix my idle to I am going to try replacing the idle valve first, before I hit the injector project. After cleaning my idle valve the Park rpms at idle picked up but drive was smoother. Very frustrating.
m

560 sel idle problem too high,rough
 

It sounds like a lot of air leaks. It most likely is from leaking seals around the fuel injectors. Plan on removing all the fuel injectors (while they are out, have a good shop clean and test them all for you--cleaning them with a good solvent flush can work wonders for bad spray patterns). Then replace all the O-ring seals on the injector holders, the seals on the injsctors, and any of the rubber air piping that has hardened (probably all of it) . A lot of individually small leaks creep in and then cold weather opens up some more and VOILA! a high rough idle results.

Parts are inexpensive, and time is not more than a couple of hours.

Update: It is a Bosch cap with numbers. I should have remembered as I replaced the cap and rotor (along with belts, hoses and water pump) when we got it last year. Anyway, I followed it to the #1 cylinder (pass front like you said).
Soo.. now comes the shocker, idle was 30 with and without vacuum, 3500 was about 45 both ways. Moving the dist far enough in one direction made it go below 20 and stumble badly, other than that no change.
I then followed the vacuum line to a little box on the driver front which I took to be the ignition control (Siemens 5kw6 144 ,004 545 5532). I thought it may be the problem and would be a good thing to have a spare of if it wasn't. I called the local parts store and they said $1200. Can this possibly be right? Are we talking about the same thing?

Check to see if the OVP is ok, you lose power to certian models of the 116/7 engines and the idle goes up, not down.



Joe

steve,
If you find an air leak around you breathers let me know, I have checked my rubber and replaced it all, I actually have a new pair of breather hoses. Changing the rubber has helped my idle but, I still have the wierd idle at park.In response to Kebowers, The only leak I have not checked for is the injectors I will try checking those at the next opportunity thanks.
martin

Question for Joe
 

Joe,
I read through the site and manual about the OVP. Mine is supposed to be the 6 pole (K1/1) according to the schematic, but it looks like the 9 pole K1/2 (ie. 9 pins and 2 10 amp fuses on top). I would like to test it as it was replaced in 96 and is from Hungary (which I believe they said was the bad one). Do you know of a vehicle that used the 9-pin that would be in my CD manual so I can look up the schematic to figure out how to test it?

PS. Thanks for the tip as it wasn't apparent to me that this had anything to do with the timing.

Steve:

I posted a similar question with my 1896 420 SEL. In my case the vacuum line to the EZL was disconnected when I bought the car. I did not find out about it until I checked the timing and realized that I was at 5 degrees instead of 12. When I re-connected the vacuum to the EZL the rpm went up as well as the timing (it went up to 25 degrees). The idle is as high as yours. I had a mechanic check it - looked for leaks but none were found. Cleaned the idle valve but it did not help.

My next step is to follow the diagnostic on the CD: Measure the current through the idle valve and check for proper operation of the throttle contact switches.

Please keep us posted on how your investigation progresses.

Leon

Leon - Sounds like when we solve one we'll have them both as mine initially was significantly improved by removing the vacuum. I am printing all the manual pages that relate to the EZL and will test everything I can. Mine has now progressed so it is 30 degrees with and without vacuum!

Joe - I think I tested the relay, + on 1(30) and 3(16) and - on 5(31) produces + on 2(87E), 7(87E), 6(87L) and 9?(87L). Should the outputs be regulated? (13.8 in gives 13.8 out)? The fuse closest to the cap pivot controls the power on 87E and the other 87L. The second fuse output has nothing connected to it. Sound right?

Steve:

I am assuming that the OVP refers to the Overvoltage relay. I did replace this relay (around $80 from the dealer) for another problem I was having. Obviously, I discoved that the vacuum to the EZL was disconnected after replacement of this relay. I now have a new overvoltage relay and my idle is high when the EZL is connected to the vacuum.

I suggest following the steps that the manual suggests. Start with the resistance mesurement of the idle valve, continue with the current measurment when engine is at normal operating temperature (current should be 700-1000 mA). If current is OK then you either have a bad valve or an air leak. If current is not OK then check the throttle valve switch, the wiring to the control unit and the other items the manual descibes.

Let me know your progress.

Leon

Leon - Thanks for the tips. I was checking things again and we have exactly the same problem. When I got the 30 degrees with the vacuum off I hadn't let it warm up. Warm I get 13 with the vacuum off. I have checked power and 750 ohm resistor both OK. I already checked and cleaned the idle valve and it is OK and doesn't affect the timing. I am running out of things to test. I am fearing the ignition control module (EZL)! Maybe I'll disconnect the vacuum and sell it! (Just kidding, I think!)
Steve

Steve:

It may not necessarily be the EZL unit. In fact, the people I spoke to told me that these units are very robust. I am not sure which resistance you checked, but I was suggesting testing the resistance of the idle valve with the engine off and the connector to the valve disconnected. If I recalled correctly is should be around 5 ohms. You should check the current through the idle valve, that the inputs to the control unit are correct, that the wiring between the inputs and the control unit are good, and that the control unit itself is good (unit is located inside the car). I am going to do all these tests on mine when it stops rainning!

The story on my car is that it was purchased by one of the teachers at my son's school, serviced by a Mercedes mechanic during that time before she sold it to me. She had not idea that the radiator was partially plugged up (not as obvious since water was flowing through it without any obvious restrictions) and it also had the vacuum advance to the EZL unit disconnected. It passed the state smog test (this was illegal since only a deviation of few degrees on the timing is allowed -the car was off by at least 7 degrees!).

So this is the story on the "professionals" who worked on my car before I owned it....This is not to say that there aren't many honest and knowledgeble mechanics out there - not just pats changer guys!


Leon

Leon - Interesting history, I think every car has a story. About dealers, I think most have some knowledgable mechanics, it's just that they are not necessarily the ones that work on your car. Before this car my wife had a '77 240D that a I got form a guy at work who had it religiously maintained by the dealer from new. When I got it the hood hinges had never been lubed and had seized and enlarged the holes. PS. my brother was a mechanic but not for Mercedes.

Now back to our problem. I have checked a bunch of things and they are all OK. The only thing out of spec (besides the idle timing) is that the dwell is low.

Things I've checked.
1. Idle position sensor.
2. All inputs to the EZL (except crank sensor).
3. Idle control valve, had it out and cleaned and tested it on the bench (5 ohm, opens and closes smoothly). At idle it draws a little under an amp (which should hold it closed).
4. Idle injector (removed connector with no change, so it is getting the gas from somewhere else).
5. OVP (didn't check Zener cutoff but power gets to all the right places).

I also had my wife put it in gear and step on the brake and the advance lessened both with and without vacuum. This leads me to think that if the engine slowed to the spec the timing might be right as the only EZL inputs are RPM and vacuum.

I am about to break down and get a scope and start scoping (a lot cheaper than an EZL).

Does anyone have the pinouts of the diagnostic connector? The print is too small on the schematic and I can't find them anywhere else.
Thanks
Steve

steve did you ever get this figured out?
m

bounce
 

Steve did you figure it out?
m

Martin, in a word no. I haven't worked on it for awhile. I think the car was running open loop. Someone loaned me an idle computer and that wasn't it. I moved fuel injection screw 1/4 turn leaner and that helped a lot. I didn't want to mess with it any more until I had a scope to set it correctly. Last week the timing chain broke so now I'll be asking a lot of questions on that project when I get to it.

usually, it will give you warnings before a timing chain breaks. just curious, did you hear any noise from the engine when starting cold in the morning ( perhaps many times before the chain broke??)