Ran across this with my 560SL. I would have a miss at idle. the car ran fine but at the light it would ocasionally miss. I brought it to the dealer and they replaced some injectors and spark plug wires. It still missed. I brought it by a 2nd time. Some more injectors and resistors.
Well the 3rd time I was pretty ticked off. Especially since they just had my E300 for 3, yes 3 weeks to fix a radio problem that they didn't fix.
They had the 560SL fixed in 2 days but forgot to call me. A week after I gave them the car I called them. ( I guess I really didn't mind I was driving a E320 loaner car, puting the milage on there car not mine) Oh yea its ready It was your distrubutor cap.
The cap was corroding on the inside of the cap, at the contact points. So check this out.
To contune this weird story. I requested a refund for the $1100. charge for the 2 previous visit. I had to sign a legal release before they would give me a refund. Well of course I have changed dealers. gone back to ******** in Dallas. I went to them for 17 years and never had a problem. Switch to the closer dealer for convinience.

Well enough of this rambling. Go check your distributor cap. Then I would check the wires, then think about the injectors.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car