85 380SE Idle problems
 

She starts up rough, but after about a minute she runs pretty good. The big problem is that most of the time she idles about 1800 rpms. A Mechanic recommedned replacing the idle box, but at over $200 for it, I was hoping I could fix it cheaper as it's my 16 yr old son's first car. Any ideas?

First check the connector thats underneath the box. They are known to wiggle loose. Several people have also said you can try to resolder the connections within the box.

Has the mechanic ruled out the idle valve itself, or other electrical problems?

85 380SE Idle problems
 

No, He hasn't. I was hoping to try the cheapest fix first and work my way up. I will take a look at the connections below the box and see if I can find anything needing repair. I also read that someone used 'electrowash' or something to that effect to clean the connections. I am still trying to identify that and try it also.

yup, I have idle problems also.


-First thing to check is the ICU. Pops right out, check for cold solder joints, clean contacts (I used caig deoxit, which you can get at radioshack) and put some die-electic grease on the contacts.

-This helped a little, but I still have problems. Next I pulled the "Air slide valve" and cleaned it (holding it with the contacts up, as to not get any cleaner on the coil inside) Cleaned with brake cleaner (Sprayed it until cleaner came out clear, not black) and lubed with ATF (atf wont ruin the coils) I also noticed that the tubing connecting the valve was loose on the valve, a couple of hose clamps took care of that.

..and I STILL have idle problems

Wow, it must be a common problem on these cars. I also have a 1985 380SE and it has a little problem.

When first started, it starts fine, but if it is cold out when you first start it and press the gas a little, when it idles back down- it idles low and goes back up until it warms up. I always let it warm up before taking off, but when I first accelerate on the road, it acts like it wants to stumble, then it clears out and does not do it again. It also always sounds like I have a slight miss (splutter from the exhaust) when idling, but the engine does not shake. Not sure about this. ???

Then, after it is warm and I restart and place in gear- I have that stalling out problem that sometimes occurs. Sometimes too when I am idling at a stoplight, it will have a sporadic stumble, as if it wants to stall. One time I made a quick stop at a light and it stalled when it geared back into first. As far as my idle goes, it seems OK, around 600 when in drive and about 750 in park, but there have been times I noticed it is near 1000 rpms when in park, but not always.

I am wondering if all of this may not be my problem too. I suppose I should take it to one of our local MB shops and have it checked.

Good luck to you!

Our W126 SEL has been in the family for 12 yrs now let me just tell you these idle problems come back every 2 yrs on average.

I had enough of the thing...nothing beats an MB from the 90s.

I'm experiencing this same exact problem.


I've done a few searches on it, it looks as if the fuel injectors/injector seal maybe to blame.

me too
 

I experienced the same problem years back on an 85 380 SE and was able to clean the idle control valve with WD40 to eliminate symptons. Shortly after, I had a valve job done and mentioned the symptoms to my A+ indie. He installed a very small piece of tubing between the two hoses on the ICV sort of like a jumper. A few years later I noticed this jumper was stock on an 87 SEL. Maybe one of resident guru's is up to snuff on this remedy?

can you provide pics?

Yeah, sounds like we have the same problem. I too would like to know the exact location of this idle control valve and how to remove. I have been told several different things....

MONOMER - does your car also stall out sometimes when you place it in gear after it is warmed up? Mine does.

Location on my 380SE is right next to distributor on left with part of it covered by the air cleaner. Its a silver tube like part, with two short hoses attached along with a plug connection. Look in Fastlane under Fuel injection and you will see Idle control valve..about a $200.00 part so cleaning it first would be my first step. Cold start valve could also be a culprit. To check disconnect it and have someone start the cold engine. Fuel should squirt out if it is working properly.

"cold start valve"?


-I didnt have to much roadtime with this car yet (mainly due to the brakes not working) so I dont know.

the ICV/airslidevalve is in the front of the engine, right ontop/near the thermostat housing. Hoses connected to mine seemed loose, which I fixed with a couple of hose-clamps.

Digital camera broken
 

Lint to ICV at fastlane with pic:
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1Q1172JL21Q216YDXW&year=1985&make=MB&model=380-SE-001&category=C&part=Idle+Control+Valve

The hoses on each end can be bought pretty cheap. Try:
http://www.mercedes-benz-parts-direct.com/

The jumper hose I referred to goes between the two hoses on each end of the ICV sort of like a bypass. Didn't have it on my 85 380SE. Indie added it by drilling into 2 hoses at each end of ICV. Improved idle. Last time I looked at a V8 (87 420 SEL) this bypass hose looked like it had become a factory stock item. If you look at the photos of the hoses for the ICV for an 87 420 SEL at:
http://www.mercedes-benz-parts-direct.com/
you can see the jumper (hose connector) and a photo of the two ICV hoses with a place for this jumper to plug in. I don't recall seeing this arranagement on pre-87 V8s. Its possible the 87 ICV hoses and jumper will give you the mod on earlier V8s. Was hoping one of our resident gurus would have popped in by now. I am not an expert on this. Just passing on what I have seen.

you think drilling the two hoses and putting a peice of (generic) tubing in will work?

Wait for an expert
 

to fill us in on this one. Seems like my indie (as good a mercedes tech I've ever met, spent many years as a master at the local dealer) used what looked like a HVAC vaccum line (small diamieter) for the mod and he knew right where to tap into the hoses for what looked like a small bypass for the ICV. Like I said if you look at a 87 or later V8 I think you will see this already done by the factory. What we need is a pic from someone who has the ICV with the small bypass tubing installed from the factory and one of our resident expert's take on the subject. Don't go drillin on no mercedes based on my say!

If you look it up on the mercedes site partfinder, it gives you a pic of what the new hoses look like.

Drilling into a couple of hoses is nothing, I can easily find a replacement for that locally if (when) I screw it up. I'm a machinest by trade, I'm quite handy with a drill (and LOVE to tinker)

A pic "under the hood" of the car that has the proper lines would be perfect.

Had a talk wit Whunter yesterday:


-Might be a ground issue, between the tranny/engine ground (he recomended a jumper from the battery's neg terminal to a Solid engine ground)

-Could be as simple as a cold solder joint on the OVP (it's the relay with the red fuse at the top)

mystery hose
 

did you mention the jumper hose at the ICV that appears in 87 and later V8s? I'm curious about this one.

I did not.

A bad solder joint seems to have been the problem for me.



Take a look inside you OVP (the relay/fuse that has the red top/10amp fuse in it)


This also explains why some of the car's other functions werent working all to well...

I have seen this bypass tube on my W126 CD but it is not on my 380SE. I too would like to know what puting one in would do..my two hoses on the idle control valve have the little extension where one of these by pass hoses could be put in but are sealed. Wonder what else was changed or added along with this by pass hose on the 87's 420's

I lied....


still has problems.




Might be as simple as an O2 sensor

380SE cold idle problem-new questions
 

Still investigating rough ilde until car warms up to about 60-80C Not as bad this morning even though it was 19 F degrees.

1. Would a "bad" tank of fuel be more noticeable in cold start than when fully warm?

2.Would fuel pressure regulator problem be more noticeable when cold?

Plugs, rotor, dist cap in good shape--rechecked condition yesterday.
fuel filter replaced this year.
New OVP and water temp sensor

Cleaned idle control valve and if I disconnect it engine revs increase so I don't think this is a problem. Wasn't very dirty either

Frequency valve buzzes so it appears ok.

Cannot find any vacuum hose problems.

Filled tank up yesterday and rough cold idle not quite as bad but it still somewhat rough till warm then car runs and idles like a dream.

Haven't checked cold start valve yet but it seems if this was a problem car would not start right up and run at higher rev abouat 1000/min then gradually drop to normal 500/min when warm.

thanks

pull the plugs
 

and look for fouling. How many miles on the wires? I would put it new plugs (bosch copper, non-resistor) and try a set of new beru wires. You might be surprised, expecially if someone installed cheap wires or platinum plugs.

plugs were the first thing I replaced. I didnt use the recomend bosch plugs, but the ngk with the same specs as it.

plug wires and dist. are new.

ICV Pic
 

started a new thread titled ICV jumper hose with a picture of that appears on V-8s starting in 1987.

just ordered those peices + hose from fastlane.


will post when they're tested.

I had another post here but it was misleading in what it solved so I did not want to send anybody down the wrong path.

I too have a 1985 380se with an idle problem. When it has warmed up thoroughly, this is when it has the issue. It is clearly noticeable in Park or in Neutral with no load. In drive, sometimes it is there. Add AC to drive and I have never felt it. So no load is biggest problem, and the more load you add, the better it gets.

I bought a CIS fuel pressure testing kit. The warm-up compensator did not pass the cold pressure test. I replaced it, the new one is in spec. exactly, that was nice to see, but... all this did exactly nothing for my idle problem.

I did not thoroughly diagnose the system, but kind of launched into the idea that the brain was dead. This was due to the following observation. When warmed up, and doing the old funky idle mis-fire thing I would watch the on-off ratio. It would start at about 1.25 volts then drop down to 0.8-0.9, misfire, and then it would bounce back up to 1.25, the engine would rev up to do this as it followed the ratio back up. Then fall down again, mis-fire would occur and then it would center back up.

I got a rebuilt lambda control unit in, pulled out the kick panel, removed the old one, dropped the little nut down under the floor, got another nut, and installed the new unit. It most definitely stopped that hunting BS. I guess I was expecting a baby smooth idle like my 2003 VW, the miss is gone but it is still not as smooth as I was expecting. Tomorrow, I am going to try and fine tune the on-off ratio to see if I can help it a smidge.

Other thing I did was after initial brain transplant, I went ahead and drilled out the rubber couplers on the ICV and installed a by-pass shunt as was mentioned. For you folks considering such a move, don't bother, that does exactly nothing other than add another couple of holes in an already touchy system that is sensitive to vacuum. The closed loop ICU will keep the idle where it needs to be. I am now guessing that when they did role this change in they might have done some other electronic adjustments to take advantage of the air flow offset, that would not be in my 85, just supposing of course.

starting problem issue is diferent at cold or hot engine start, when it hard to start cold engine you must check fuel pressure before starting the engine , if it is not sufficient your problem is in fuel pressure check valve at fuel pumps($30 each) , if the starting problem is at hot engine your problem is damper($180) , that is the cone type aluminium piece next to pumps. if you have one of this problems - it is real meaning that your fuel pumps are weak and need help , first remedy to it will be ATF to the tank to lubricate them.
irregular idling will be a different problem, but you can not jump to that before fixing fueling problem.
good luck

I had an idle problem with my 380SE. It would not idle at all and then it would idle high. I accidently smacked the ICU on the firewall with a screwdriver handle and it died. Thinking it might be a coincidence, I started the car and smakcked the ICu agin...same result. I went on Ebay and bought a good used one and everything has been fine since. No high idle and it idles where it should in park or in gear.

The cross over vacuum line does go between the "Bumps on the hoses that are not drilled. I got the smallest ID vac line from the auto store. However I didn't install the line yet, because my problem was fixed by the new ICU.

Thanks guys. Honestly, I'd hold off on installing that vacuum line. I'll keep the forum posted on how mine is working out, but like I said, I have seen no idle difference with it installed.

Good tips on the starting. My car has always instantly fired right up. My measured system pressure is perfect as is the cold control pressure and the warmed up control pressure.

The lambda control unit replacement seems to have fixed the rough idle, but I can not declare victory yet, I need to drive it a few more days.

That is interesting about the ICU. I just had a rough idle, it did appear to idle at the right speeds at the right times, so I have never suspected the ICU or the ICV except early on when I was just starting out, that is the reference to the misleading post. I removed the ICV, cleaned it out and reinstalled and had claimed that fixed the problem. That was not true, I was just not patient enough to realize the problem was most definitely still there.

I warmed up the car good with a short drive to the store, got i back home. I am going to declare victory on the rough idle. I did one last fine tune of the on-off ratio. It still oscillates just a small bit, but the value is in the exact same range as at 2500 rpms. I can also trim it out anywhere by turning the screw, it is neat to see the control system adjust the ratio to compensate for the richer or leaner mixture. So now I know it is doing what it is supposed to.

Many causes for a rough idle. I replaced:
1) O2 sensor (just because)
2) Warm-up compensator (failed cold pressure test, not by a little bit either, it was clearly off), new one was right in the middle of the acceptable band for temp I took the reading at.
3) Replaced the lambda control unit. The old one was malfunctioning with a wide swing hunting for a value.
4) Added the shunt line around the ICV, I don't think this was necessary and I noticed no difference in idle.

Interestingly, the car seems a touch more sluggish now. I guess without that rich charge getting blasted into the engine with no compensation, it is just not as peppy.

Summary VICTORY over the rough idle.

I thought the ICV bypass was to help the random stalling problem that some people, including me, were having. I put it on mine, but it doesn't seem like enough air would go through to affect anything. All the same, mine hasn't stalled at all lately but I'm not sure if it's strictly due to the bypass.

You know that is a good point. The shunt was to correct for stalling after breaking, etc.. and had nothing to do with rough idling. I have had a stall or two on occasion just like yourself on others, we'll see if it ever happens again now that the shunt is installed.

Have you checked temp sensors?
 

Sometimes a high idle can be related to the temp sensor not being read right. The engine will adjust fuel trim and then make the engine run at higher RPM. It could also be a bad fuel pressure regulator. Check all of these they are cheap to replace.