380SE high idle, still. Totally stumped!

[finn]

380SE -85. Lost idle at first, then the work done:

-New idle control valve
-New idle control unit
-New throttle switch, replaced a year ago, tested now, almost zero ohms at idle; so it closes, fine
-Temp sensor tested: pulled the connector with warm motor, no change in idle speed, fine
-No significant vacuum leaks

Rpms cold: 750 in D/R, 900 in P/N OK
Rpms half warm: 500 in D/R, 650 in P/N OK
Rpms warm: 550 in P/R, 900 in P/N NOT OK

What can I do now? The repair manual doesn´t help anymore. Take it to the real tech? I appreciate your help!

Here´s what have happened before:

Used idle valve from dealer !

Idle control valve broken?? W126

[finn]

Sometimes it will idle 650 rpm fully warmed in P/N but then the idle creeps up to 900 rpm! Any clues?

[Mike Murrell]

Here's another site you can search:

http://www.mercedes.cx/archives/mq.html

I dug around there and found more than one post that attributed a high idle on the 380 to the infamous OVP - overvoltage protection relay.

[finn]

Thanks Mike, but the problem was elsewhere. It is however solved! Here´s the story:

I went to my trusted indy to the regular maintenance. Mentioned the high idle and he shortly find that the hose clamp between mixture control and throttle assy was loosen and broken. So it would leak air after engine has warmed up and then raise idle. He told me that the one who replaced the throttle switch is responsible for the broken clamp. It was the dealer who did the replacement.

I went to the dealer and insisted that they would replace the clamp under warranty. They really resisted but eventually agreed. The new clamp did not cure the high idle. But the dealer found that the ignition timing was 13 degrees off the factory spec!!! The timing was adjusted to spec and the idle is now perfect!

[Ghanouni]

Had this problem. Replaced the OVP fuse which did not fix the problem. Ordered an OVP from GEEK. It just arrived and is installed. The problem solved. Idle back to normal and ABS light off. Thanks for posting your experiences on this forum. Very helpful. This repair could have cost me over $600 and was solved for $85.