I have a 1985 380 SE Euro Spec Benz. I took my car into the Mercedes Dealership because my car's idle was irregular. I checked the air slide, and it was functioning properly, and the mechanic at the dealership told me that my idle speed control was the culprit. He told me that it would be about $500 for part and installation. When I looked at the part that he was referring to it seemed that I would be able to install this my self. I checked with the dealer and was told that the part cost $291.50. How difficult is the install? How do I do it?

Thank You in Advance for Any Advice!

It's not that hard. It's located "behind" the glovebox. The interior of the glovebox is held in place by some gray fasteners, on your 85 they should be plastic button fasteners. Once the inside of the glovebox is out, you'll see the relay, it pulls straight up and out of the socket, then the new one, once aligned with all the electrical sockets, can be pressed down into the connector.
Gilly

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My 380SE -85 Euro had intermittant high idle about 1000r/min. I went to dealer and mech told me that idle control valve was bad. The price of valve is $600...so I cleaned the valve with carb cleaner.. after cleaning it worked properly. But the car still idled high.

Then I took out idle speed control unit, located in engine compartment between engine and the firewall. There was some components with bad soldering. After resoldering of loosen legs the unit seemed to be fine.But the high idle was still there.

Finally I studied the Service-cd very closely and there was told about measuring the condition of throttle switch. I checked the continuity, idle contact of the switch. I found no idle contact! The throttle switch was changed and idle came back to normal. The switch price was $35.

Good luck.