Car: 1989 260E, 198,000 miles


I noticed my car was idling at approx 1000-1050 in gear, and 1500-2000 in neutral/park.

I immediately searched Mercedesshop for causes. The consensus was to check the following:

Throttle Linkage
Idle Control Valve
Idle Control Unit
Decel micro switch

Since it was late, and dark I focused only on the linkage.

After removing the air cleaner, I blasted the linkage components with carb cleaner. They were fairly dirty and a bit grimy. I did not disassemble anything since I was not sure how.

While cleaning, I noticed the micro switch with its little roller, and saw that the flat part of the metal linkage that is supposed to open and close it was *under* the switch arm, rather than against it. The switch also appeared to be the grimiest part of the linkage.

With the engine running, I manually moved the linkage to rev the engine. In the “rest” position, the engine slowed, and idled normally (approx. 550 rpm) when the linkage engaged the switch properly. It also seemed to idle normally when the linkage was not in contact with the switch, i.e. when it slid under it.

Also, the little “button” the switch arm is apparently supposed to push in and out did not appear to be moving. In fact, it appeared to be pushed all the way in.

When manually tripping the switch with the throttle linkage moved off of the switch arm, open, the engine did not drop to idle speed. Then again, I was not revving it that high, so it may not have had anything to drop to.

My assumption is that the switch is so filthy that its moving parts have either jammed, or are very gummed up and move much slower than they should.

After replacing the air cleaner, the car idled normally (550 rpm) in neutral and in gear. This continued after a test drive as well.


As of this morning, the car idles at 950-1000 – both in gear and in neutral/park. My assumption, again, is the switch. Perhaps some of the gumminess was loosened by the carb cleaner, but is now starting to stick again?

I am not unhappy with this condition, however. I am actually quite pleased with it. My Economy gauge is at Zero when I am idling. Shifting is a bit smoother and quicker. Engine is running cooler.

So, if the idle says in this range, should I leave it alone, or would there be potential risks involved?

I realize I need to replace the switch, and will do so after the weekend. Unfortunately, if it really is the culprit, there goes my acceptably fast idle.

But if the problem is not the switch, am I correct in assuming the linkage is too sticky (whether from dryness or grime) is the culprit and I need to properly disassemble and clean it?

If so, what is the correct way to disassemble the linkage parts? There appears to be one or more loose metal sheaths with spherical ends covering what I assume are the linkage arms and (ball?) joints. Do these sheaths simply lift off?

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black