Idle Control Valve Wiring Problems - Mercedes-Benz Forum
 
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#1 (permalink) Old 03-23-2013, 02:12 PM
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Idle Control Valve Wiring Problems

I've been having high idle problems with my 380 for a while now. I've had both idle control units looked at, one needlessly replaced, tested and the idle control valve, and tested the wires that go to the idle control valve. When I put a 9 volt battery to the connectors on the idle control valve, it shut right away so I know that it works. I tested the wires that connect to the idle control valve and when the battery is connected but the engine isn't running (the valve should close) there was no electricity going to the valve, with the engine running there was only about 1.3 volts.

The conclusion I'm coming to is that the wires that lead to the Idle Control Valve aren't properly connected. If anyone has had this problem or thinks they know what I need to do to fix it, any help would be amazing. Or if someone can tell me where those wires run so I can check the connection. Thanks.
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#2 (permalink) Old 03-23-2013, 09:14 PM
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The wires tend to fatigue and break right where they enter the plug that connects to the ICV. On my '85 there was only 1-2 wire strands remaining on one of the two wires. Easy to re-solder once you get the pins out of the Molex connector.
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#3 (permalink) Old 03-23-2013, 09:58 PM
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Idle Control Valve Wiring Problems

I redid the connectors on that end about a month ago. I think it's the other end that's faulty, I just don't know where and what it connects to.


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#4 (permalink) Old 03-24-2013, 02:09 AM
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Idle Control Valve Wiring Problems

1986 560SL idle speed air valve wiring is:

Air valve pin1 goes to idle speed ctrl unit pin6, black/yellow wire
Air valve pin2 goes to idle speed ctrl unit pin7, black wire




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#5 (permalink) Old 03-24-2013, 02:11 AM
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Idle Control Valve Wiring Problems

And the schematic


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#6 (permalink) Old 03-24-2013, 02:13 AM
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Idle Control Valve Wiring Problems

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#7 (permalink) Old 03-24-2013, 07:51 AM
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I've just come thru high idle hell with my 85' 38SL. Couple observartions: when you switch the ignition on (but do not start the engine) there should be some DC voltage (I don't recall the eaxct voltage) to the idle control valve and the valve should actuate. Positive DC voltage is supplied to the top (black / yellow tracer) lead going into the valve, although it is really not important if positive current is applied to the top or bottom wire.... This is becausee when the engine is starting there must be a slightly enriched fuel mixture.

If you are getting zero voltage with ignition on that is a symptom. The 1.3 volts when running seems not sufficient to operate the valve properly. I am assuming your idle problem is around 1900 RPM?

Current to operate the idle control system comes from the Over Voltage Protection module. Check to make sure you have 12 volts coming off that module to the idle control module. If you don't, try bypassing the OVP module and run 12 volts direct to the control module. If your idle returns to normal you found your problem and just replace the OVP module.

If voltage from the OVP is normal, next consider that there is an oil temperature sensor which sends a signal to the idle control module to help regulate idle speed. However if that fails the result is your engine will idle around 800-900 rpm which is higher than normal for fully warmed up but not the 1900 you get when the valve is not actuated.

Next, you have to consider whether the throttle switch is working. The switch is located on the side of the throttle plate and interconnects to the idle control model via a cylinderical plug which is found in front of the washer fluid reservoir. Sometimes if that plug has been unplugged a few times the guide notches will break off and it is possible that the plug can be plugged together in the wrong position so that the throttle switch is incorrectly connected to the ICM. Under good bright light, look carefully at that plug to confirm that it is properly connected. If it is, try unplugging it and jumper the two pins which take the current from the throttle switch (you jumper the plug which runs to the ICM, not to the throttle switch) and see if idle drops.

Beyond this you may have an open or short in the wiring of the idle control system. But these are good things to look at!

-George-
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#8 (permalink) Old 03-24-2013, 09:46 AM
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First: What are your symptoms?
Just a suggestion: try the throttle switch first! It's easy to diagnose. Mine was bad and I screwed around with all the rest until I took it to my indy and he discovered the problem. I did the repacement and it wasn't bad, as he wanted $1500 and told me that I should do it.
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#9 (permalink) Old 03-24-2013, 12:56 PM
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Idle Control Valve Wiring Problems

I know someone that used to work as a MB mechanic so I'm going to ask him to fiddle around with it I think. I haven't looked at the OVP or throttle switch but I think those 2 are the next things on my list. As for the idle speed, it's at a pretty constant 1500 and the only time it goes down is when I put it in gear but that only brings it down to 8-900.

Last edited by Stashman94; 03-24-2013 at 01:07 PM.
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#10 (permalink) Old 12-21-2013, 11:58 PM
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So did you ever find the problem? Why do people start threads, ask questions and never update their resolutions?
This really messes up the whole point of car FORUMS!

Ski

new girl 1985 380SL

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1983 BMW 320i-build thread- http://forums.bimmerforums.com/forum...0-build-thread
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