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Old 08-28-2017, 11:09 PM
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Join Date: Aug 2017
Posts: 1
Question High Idle and AC compressor?

I know it's been discussed to death already, but my 87' 560sl suddenly developed a high idle in P/N after 10sec of starting the car. (in Drive, the rpm drops). just a day or two before I recharged the AC with 134a for the first time and the ac compressor started to work as I charged the car. (AC works great). Soon after (a day or two) the high idle started. Is is possible the resurrection of the AC compressors caused some electrical gremlin to cause this high idle? I checked the electric connector to the Idle control valve terminals and I don't get 12v. only 2.7. I checked he OVP and the fuse is fine, even changed to another OVP I had around. no change.
Is it the Idle speed control unit behind the glove compartment? I did wiggled it a bit and even took it apart to see if any of the circuits is damaged (none), but the idle did change a bit as I wiggled it) I even disconnected it completely while the car was idling and the idle went really higher, so it's doing something.

So the questions are:
is it Idle speed control unit ?
Is it the wires?
Is it any one of the temp sensor? (coolent/oil)

Many thanks for any help
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Old 08-29-2017, 09:13 AM
Diseasel300's Avatar
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Join Date: May 2016
Location: Texas Hill Country
Posts: 4,666
The idle control unit is a box behind the glove box. They're famous for having solder joints break where the pins attach to the circuit card. My SL did this and it drove me crazy, finally got to the point that it just ran 1500RPM randomly, usually as you approached a stop light. Not fun trying to stop when it was doing that. If you're handy with a soldering iron, resolder the large pins where they connect to the card. Fresh solder helps a lot.
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