You did not state anything about a hot/cold engine. Engines shake more noticeably until at operating temp.

Perhaps you notice that shakes as the car is warming up but then notice it smoothing out when it reaches temp?

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD