Obviosly take M.B.Doc's advice before mine!
However, it wouldn't be a bad idea to take a look at your egr valve and the hot inlet pipe.
Stevebfl has posted that he reams out this pipe as part of the 60,000 mile service.
There was also a TSB on the original EGR valves that commented on a sticking problem.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".