I recently bought a 1993 Mercedes Benz 300e from a private seller, it has 190xxx miles on it. The car runs good but when it is stopped the rpms drop below 900 and it has a very noticable vibration which goes away when I accelerate. There is no smoke or signs of an oil leak but there is a mild smell of something burning (especially hwne your behind the car). Anyone have an idea of what this could be?
The first step should be running a compression test as one low cylinder can cause a symptom like this. Hopefully the compression will be fine and the problem will be comparatively minor; ignition components, vacuum leak, etc.
The reason for the compression test is to weed out a mechanical fault as it is very easy to throw a fortune in parts at a problem like this and never resolve it.
Normal idle speed for most cars these days is about 700-750 RPM. Why do you want this engine to idle at 900 or more?
In addition to ok4450’s recommendations, which I agree with, as always, you might want to look at the Idle Air Control (IAC) valve, and associated parts/systems.
I hope you have a working relationship with an independent mechanic who knows MB cars.
Thank you ok4550 & mcparadise. I will have my mechanic take a look at it.
Oh yes I did fail to mention in my first post that sometimes when I start the car to let it warm up it will do its normal vibrations, rpms drop and it will stall (its an automatic trans.)