TO all those who kindly replied to my thread re: rough idle problem in my 91 420SEL --

Problem solved by replacing the spark plug wires (originals were 13 yrs. old) and the distributor cap and rotor (all Bosch parts -- from MercedesShop). Just purrs......RUNS GREAT!!

Of course, per your suggestions, I first checked out the O2 sensor, the vacuum lines, etc. the easy, obvious stuff before spending close to $ 300 bucks on parts!

Again,, thanks much!