Ok guys.. I'm lost and have no idea what to do next. I have an 87 560SEL. The car runs beautifully, but when at an idle it wants to stick around 1200. When it gets warm, it wants to peg at 1400. In drive it will drop down and stay at 850. There is no miss or rough idle. The fuel/air mixture is 14.7/1 which is exactly what the factory specs are. Replaced the air vacuum contor module. No change. When slapped on the computer, the exhaust is blowing at 0. It just wants to run high in idle. Any help would be greatly appreciated. I love this car, but it is eating me out of house and home. I'd kick it, but that would dent the perfect paint job. Help!!!!

I checked all of the vacuum lines and found no problem. I even took it to a shop where it was smoke tested. No leak. The mechanic was even stumped at what to check next. Any suggestions?

Check idle control valve????
And maybe a different mechanic??

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My '86 420 idled high when I got it, exactly like yours. I replaced a little black box (the idle control) which is located under the passenger-side toe board/carpet, and it has idled perfectly correctly for 5 years now.
Once you rule out air leaks, etc., look at this. I hope this helps you.

Can the idle control be fixed or should I just try to find another one?

And is there a way to test it while it's on the car? If so, step by step directions would be greatly appreciated!! Thanks!!!

With engine running, unplug it and see if the idle does anything different. If it doesn't change things, one of the wires on the control valve should have voltage, the other one is grounded via the idle control module. If there is no power on one of the wires to the valve, you need to trace the wire back, I believe the voltage originates at the ovp, or possibly the engine control mod, but pretty sure from the ovp, have you checked the ovp fuse? (that's overvoltage protection relay, over near the battery, with the clear lid on top and the fuse under the lid)
Gilly

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unplugged it. idle ran up around 2000. plugged it in. came back down. checked the ovp fuse. it was good. what should I be looking at next? I feel like I've been throwing parts at this thing and although the idle control valve cured the miss that I was experiencing, it still seem to me that it is idleing higher than it is supposed to.

No one monkeyed with the linkage and now the linkage is being pulled? People dink around with that stuff all the time not knowing enough to leave it alone.

Gilly

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Gilly;
I didn't understand your last post. Linkage? The only thing I unplugged was the plug into the vacuum control module.
JD

JD-
Randy had the right suggestion. The idle control unit is likely the next thing to replace. I've got a few from the local yards-- they run a couple hundred new, but yards have them for generally $20 or $30. If you have a friend with a w126, you can swap out to check, but that's the only way to "test" these things that I know of. I can send you a known good one.

Beyond that, it's a bit of a pain to track down a high idle, but vacuum leaks are the most common culprit. Replacing the air distribution lines is what finally fixed my problem. Around $100 for those from ********AZ.

Here's a link to look through:
http://www.slack.net/~thundt/mercedes/high_idle_hell.htm

And this-- look at posts #63 and #64
http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1340751-do-yourself-diy-repair-thread-wheel-2.html

Good Luck!
Dave

I didn't mean YOU monkeyed with the linkage, prior owner or a shop?
They'll try to fix various problems by screwing with that linkage. It's never the linkage. Unless someone screwed with it.

Gilly

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Gilly: Thanks. I checked and the linkage doesn't look like it's been messed with, but I don't know enough to tell definatively whether somone did or not.

ElRojo and Randy; I think that the idle control unit is the next thing to occupy my day off with. Is it under the passenger side toeboard on a 87 SEL. Also, my wife drives a 89 300SE. Would her idle control unit work to test mine? (I've gotten hers running perfect)

Check your PM...

The six cylinder idle control will not work, I think. I'll check out the part # for you.

Dave