hello John, this is your lucky day!!!

Actaully, high idle is the most common problem on these cars. I would suggest that you get a couple of your favorite drinks and do a search with "high idle". It may take you 3 days to finish all the reading.

With what you read, you could start to diagnose your car one source at a time. Report back what you found in details and see if we could talk about.

I have been fighting the ghigh idle issue on my 1991 560 SEL for the past three months. It could be good for a coupel of days but most of the time it runs just like yours.