Hi, I just bought a 1987 mercedes 420sel and it has a few issues. My main issue is when I start the car it idles at around 300rpms (and sometimes dies out) and then after about a minute it revs up to 1000rpms on its own and then goes back down to around 700rpms(normal idle). Im very new to these cars so im not sure if this problem is common. If anybody has any input on how to fix this problem it would be greatly appreciated. thanks

 

yeah theres not much support

i've asked the same question but on a 500sec, ive gotten no answer in a week

 

I am not an expert but have 4 MBZ right now. First suspect from my own point of view would be the Idle Control Valve, about $440.00 (plus tax) when new from the dealer.
This isNOT a pinpoint problem and not from an expert. I am only responding from my own experience and since you have not gotten a response yet on your question.
Please ask a qualified mechanic with the aid of required test equipment to pinpointthe problem. And if the problem would be the Idle Control Valve, I could help you with big savings on the part.
Nes

 

i think the problame is the ovp relay behind the battery on the bulk head hope this helps

 

bandit.1200 post is very valid. I brought one of my MBZ to an independent MBZ garage and without hooking up a test equipment, they tried to put on a new OVP relay. It did not solve the problem though, but it is very telling and was told this simple looking relay could be the culprit for an out of spec running engine. Anyway, I was told my ECU was not communicating that they were not able to pull out any error/fault codes. Now, I got two spare ECU's. Anyone who needs MBZ and BMW parts, I could help.
Nes