My car, a 99 E300 Turbodiesel, has the exact symptom on decelleration. I have an additional feature which is a "miss" or intermittent rough idle only when the car is at operating temp. and only while in neutral or park with no elctrical load. Switch on the climate control, headlamps, seat heaters, and the car idles normally. Thus the techs have ruled out a bad IP as the source for the roughness. The car runs too well for this to be more than an annoyance, but clearly something is amiss. The rough idle is a relatively recent development that coincided with an alternator relacement, but the decelleration issue has been with me for at least 50,000 miles. So if you can live with it, it is probably not likely to hurt your car in the near or long term.

The EGR bypass will be tried as a fix--hope it works.

Steve