Hey guys,

Some rather odd news from my indy today. I had him hook up the car to the lambda to tune her up after my distributor and plug install, and my idle, despite new Idle Control Relay, Vac components (They smoked it as they thought that was the issue at first; nothin.), EHA and OVP... The car's idle still 'revs' in place, and decides on its own when a disconnected module or plug will affect its function. We decided that the only possible source would be the ECU, which up until now, has been the only original module I thought was bulletproof in my car. He actually told me that my car 'was possessed'.

So I take out the carpeted sections and lo and behold, the ECU is slightly wet

How do I take it out and open it? Would these symptoms be caused by a faulty or malfunctioning ECU? And more importantly, where the heck could water be leaking from to get there? Firewall? Sunroof?

I replaced my windshield earlier this year, so it definitely ain't that.

At least, it better not be.

Thanks again guys,

Carlen

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1987 560SEL (210,000 miles)

Are you saying the idle speed is the problem?
Or does the mixture have an issue?

The 2 systems work independent of each other.

In fact if the basic mixture is "close" then the car should run 99% just fine with the fuel computer disconnected.

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MERCEDES Benz Master Guild Technician (6 TIMES)
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44 years foreign automotive repair
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Carlen, I would suspect the windshield as the source of the water leak.

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Fred Hoelzle

Both! The computer that talks to the Lambda (at least as far as I understand its function, not even sure what to call it.) is most definitely shot. He was unable to get the ratio to respond to the lambda at a consistent manner.

My idle speed also suffers, but I think that has to do with a bad ICV at this point. I suspect my coolant temp sensor or thermostat is shot too, as my temp gauge jumps all over the place. When it is steady, however, it sticks at 85 ish.

The weird racing issue to my understanding is due to that 'computer', though.

Also, just took it out of the car, and... the pins look like minature statues of liberty. They are so corroded that when I took a toothbrush to the pins, a massive pile of oxidation came off. Almost certain this box is bad, now...

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1987 560SEL (210,000 miles)

Unfortunately I think so too... Should I take it out to replace the seal, or should I use silicone under the trim?

Side note, I'm deathly afraid of bending said trim, how do I get it out?

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1987 560SEL (210,000 miles)

Uh... My idle is basically perfect (700 on the spot) without the unit...
Put it in gear, right at 550. A/C on Park, 600.

What gives??

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1987 560SEL (210,000 miles)

I think I might come to just the opposite conclusion. If there was a great deal of corrosion on the connector, maybe the problem was just a poor electrical connection, and not a bad ECU.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

I had hoped that was the case, but when I plugged it back in after sanding the corrosion off with 2000 grit modeling sandpaper, it was the same song and dance. My brother borrowed my torx heads and I want to open it up to investigate, but he doesn't remember where he left them

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1987 560SEL (210,000 miles)

Well I cant help with the engine, but the trim is not too hard to take off. I just did this myself. I will describe just one side.

First, so you do not forget, slide the "cover" plate that it top dead center. It covers a gap in the trim. Mine just slid over.

Next open the hood to have better access to the plastic grommet holding the base of the trim to the fender. I had to be a little aggressive with it.

Then I removed the side trim screws. That big rubber seal folds towards the windshield. Behind it you will find 3 or 4 screws (pretty sure just 3). To locate where they are hid behind that rubber look for small lines cast into the rubber. There is a screw behind those indicators. BE CAREFUL when removing the upper or last screw. The trim has a very weak "head pin" spot welded to the body that the trim hooks onto. Mine was broken off. It attaches like a smoke detector in that the trim has a round hole with an offset slot. And think of the head pin like screw head. I hope that makes sense. Once its off that pin it will slide down and out of the upper trim part.

The upper trim part is held in with pins like I described above. I had two, both broke. So when removed the retaining clips came along for the ride. So I am not sure how it normally comes out. But it should come out pretty easy.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

And maybe I skipped it, but have you cleaned the idle valve? Also I had a weird idle when i first got the car. It was a green vacuum line with a yellow stripe that connected to a short rubber tube just under the front of the intake and behind the dist. A couple lines run that way. Maybe it was a repair, but it has come undone a couple times. When I have an issue, its the first thing I check.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Crystal clear. I'm gonna check this out tomorrow morning and seal her up hopefully for the last time. I'm mostly intrigued as to the path of the water, as it has not come through those spots you mentioned in your interior water issue in many, many moons...

What should I use to seal it? straight silicone?

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1987 560SEL (210,000 miles)

Man... If I even began to describe the processes I've done chasing my idle... I changed every vacuum line and boot, most relays, cleaned every contact, etc... I had cleaned that thing so many times praying it would solve my plight... I bought a new one and should get here soon enough to compliment my control relay...

When I bought the car, it ran perfectly. It sat while I was learning to drive (I bought it when I was 16 from my uncle), and I assume sitting did a world of hurt to it. Thankfully, it made me change out all the rubber and aged bits before they really gave me issues.

Only vac line I have yet to reconnect (was disconnected when I started the whole ordeal) is the one coming from the top of the EGR. NO idea where that thing plugs into.

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1987 560SEL (210,000 miles)

Cant help with the EGR, not sure where mine even goes! lol

By the way. When testing lambda (which I do on my own). One disconnects the purge line. At least it should be. Its larger than the usual lines. Solid black plastic with a white line.

I found that I have a leak in my tank purge system. When I have this line disconnected at the driver's side fender, the car runs like a top. With it on I had bad fuel economy and high RPM issues. And my duty cycle was all over above 2k RPM. I dont think its your issue, but we have similar cars and similar things can happen. Just something to look at.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car