85 380SE Idle problems - PeachParts Mercedes-Benz Forum

mustangamer · #1 01-31-2006, 09:32 AM

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?

raymr · #2 01-31-2006, 09:54 AM

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?

mustangamer · #3 01-31-2006, 09:59 AM

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.

Monomer · #4 01-31-2006, 08:27 PM

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

86560SEL · #5 01-31-2006, 09:44 PM

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!

BenzOnline · #6 01-31-2006, 11:13 PM

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.

Monomer · #7 02-01-2006, 02:44 PM

Quote:

Originally Posted by 86560SEL

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. ???

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.

Chadahar · #8 02-02-2008, 12:07 AM

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.

elolson · #9 02-02-2008, 07:23 AM

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.

elolson · #10 02-02-2008, 11:02 AM

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.

raymr · #11 02-02-2008, 11:30 AM

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.

elolson · #12 02-02-2008, 11:59 AM

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.

kchemers · #13 02-02-2008, 12:09 PM

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.