Michael, there are lots of reason for rough idle.

Could be a vacuum problem, or could be a problem wiht the injectors.

Do a search here under rough idle and I am sure that you will find many suggestions.

Good luck.

(I used to own a 1991 420SEL and I absolutely loved that car, especially out on the open road).

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Current Benzes

1989 300TE "Alice"
1990 300CE "Sam Spade"
1991 300CE "Beowulf" RIP (06.1991 - 10.10.2007)
1998 E320 "Orson"
2002 C320 Wagon "Molly Fox"

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