My 85 380SE with approx. 131,000 miles idles smooth as silk. Can't even tell the engine is running. I know the PO replaced all the engine and tranny mounts and shocks. Even if yours are new it is possible you have one or more defective parts. Even new parts are occasionally defective.

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280