This is a shot in the dark, since my experience is not with an MB - and not even a diesel! The symptom would be intermittant, but most likely and severe after a long deceleration.
On my Acura Integra (180k+), I have twice had to disassemble and clean the throttle body because the throttle butterfly valve sticks. This is due to build-up of a sort of varnish, which puzzles me, since little fuel vapor should be present here. It DOES completely cure the problem for quite a long while.