I have a 1987 560sl, and about a month ago it started to idle at1800 rpm with no warning! the next morning it wa back to normal, no problems.
Last saturday (halloween) it started to idle high again, only this time it keeps on doing it. I checked the high voltage saftey relay, fuse ok, solder joints appear to be good, now I removed the idle speed control module from behind the glove box. Any body know what I should check on this module, or could something else becausing the fast idle? Any help is greatly apprecited, anything to avoid the dealer!

Thanks much,
-ddayme

The solenoid valve might be sticking.
It's located on the top of the engine at the front, slightly to the left as you look (the car's right).
It's a cylindrical device about 5" long and 1.5" wide and secured by a "p" clip.
With the engine running give it a tap with a light hammer and see if your problem is cured.

Before you starting pulling or replacing expensive components (or get out the hammer) inspect all of your vacuum connections. High idle is a common symptom of a leak.

Look at your "economy" gauge. It should be pegged to the left at idle. If it is not a vac leak is certain. Redardless, look closely at your soft rubber vac connectors. Don't forget the hidden one between the intake manifold and the firewall. It is often the first to go because of the hot, oily environment.

Whatever cures your ills, please post the repair so we can add to the data base.

Okay, I'll try with the vaccum leak check first. One thing though, since I posted this yesterday, I removed the idle speed control module and went over the connections, put it back in and same thing. I began to tap around different connections, then started the car-highidle, then it went down to normal idle speed for about 6-7 seconds, I theheard what sounded like a relay "click" and it went back to the fast idle thing.

I just now thought that I will take some pictures of what I am "messing with", and hopefully be able to attach them to a message, that way maybe it will be easier to explain/show what I am doing! give me about 30-40 minutes to figure this out.

Pull the connection from the idle control while the engine is running. If the idle doesn't jump up, that's probably your problem - either the signal to the idle control or the valve itself.

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.

my 86 560SEL just started idling fast about 1200 RPM. fuel economy meter pegged to the left. i pulled the connector off the idle control air valve while engine running and the idle increased significantly

so ... does that mean air valve is OK or could there be issues with it.

a few days ago i sprayed the engine down with some water and degreaser just to clean it up a little. did i mess something up???

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R Martin
Dallas, TX (Addison)

86 560SEL, 128K

If you pull the connector off the air valve, and the idle jumps up, you valve and control are probably functioning.

With the engine running, spray gumout carb cleaner all around the air hoses on both side along the valve covers, and under the plenum where the cross hose goes. If idle changes while doing so, you probably have a leak in one of the air distribution hoses or one of the vacuum hoses.

All new air distribution hoses will cost you about 125 and an hour of work. Hopefully, you simply knocked a vacuum hoses off somewhere.

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Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport

Good Job. You will probably find that lots of problems on W126 cars are caused by bad solder joints. I have seen them in just about every system.

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-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition

I tried that while the engine was running, but no difference. like I mentioned before, it did this a month ago,and then stopped. last night, it started and idled normally for a few seconds, then I heard a "click" like a solenoid, and then it went back up to the 1800-2000 rpm idle speed.

The click could have been the idle air valve slamming back into the home (full open) position. Check voltage at the connector.

__________________
A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.

some control box marked"temperaturereggularar i noticed that the connections to the plug from the pc board are broken, possibly by me when tapping aroud, but i doubt i tapped that hard! i also removed the overvoltage protection relay and the idle speed control module and i re-soldered a few suspect looking joints. is it possible the broken "temperaturereggular" module has something to do with this?

thanks!

what should the voltage be? and is it with the engine running, off, key on or etc? i'm so upset about this my brain is not working right!

I don't have any info in front of me (I will in a couple hours) but 0 volts would be a good clue that it's not recieving a proper idle control signal.

EDIT - looking elsewhere on the forum, you should be seeing around 4 volts.

Oh, and KOER

__________________
A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.

while running, the voltage is .006!, not even 1 volt when this happened last month, it only lasted for a little while, wnd last night it went from high idle to normal or about 6-7 seconds. does the signal voltage for the idle control solenoid come from the idle speed control module? maybe i should go over some more solder joints? if i can't fix this car, iwon't get fixed, can't afford the dealer (whom i know, and would definatly get me for at least a grand or two)!