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Fast idle

I have a 1984 380SL and misfires badly when it is cold. It has to warm-up at least 10 minutes before I am able to drive it. Any suggestions on what might be the cause?

Not familiar with the tech used on that car, but most of that vintage have some kind of air valve that opens wider during cold temps, and closes as the engine heats up. Allows more air into the engine when cold, which increases idle speed, then idle speed lowers as it closes. First suspect would be something wrong with that. Sometimes this is called the IAC (Idle air control), but it is also called other things, like auxiliary air control, air valve, etc. If this is a carb’d engine, something could be sticking or leaking in the carb or its vacuum control.

I’m not a Benz guy but this car should have CIS fuel injection on it. My condolences… :slight_smile:

The post is a bit unclear about the high idle part as that could mean it’s idling fast on its own or that you’re having to depress the pedal to keep it running until warmed up.

The former could mean a problem with an idle slide valve which I’m reasonably sure Benz uses instead of an Auxiliary Air Regulator and the latter could mean a vacuum leak. CIS systems are sensitive to air leaks so my recommendation would be a thorough inspection for air leaks as a first step.

If there’s not a Benz expert in your area you might consider searching out someone familiar with older VWs, BMWs, and Volvos as they all used various forms of CIS at one time.