1989 300CE 182K
Have experienced the common racing/stumbling idle problem before. Fixed it once with a new OVP, another time I found a vacuum leak.
This time I checked again for vacuum, no problems, then I cleaned and lubed all the whacky accelerator linkage - still running weird. After reading a few threads here I ordered a new coolant temp sensor (from Phil at Fastlane). Not a cheap part @ $65 or so. I put it in and my sweetie is running better than ever. Easier warm start, smooooth idle like the in-line six should be.
Just thought I'd pass it along.
By the way - Thanks again to Stevebfl, Larry Bible, Haasman, Schumi, Psfred, and all the others who have helped me keep this nice car nice.