That involves some historical info, did you replace your engine wiring harness yet? That can cause a lot of strange problems. Jim had some similiar issues with his S coupe, take a look at his site and see if you can find any information,
http://pages.prodigy.net/jforgione/MB_S500.html See if that will get you started. I am not totally familiar with those cars, I have most experience on OBDII autos, except for the things I have seen on the site and from friends in the MB club. My advice is that if you have done everything you can, take it to the Dealer and have them do a diagnoses, they have a specific machine that will tell you exactly what is wrong, and they see those cars every day. Good luck!
Brian