I drove a 02 Clk 320 for 2 months trying to diagnose a sporatic
fault on a buy-back car. I noticed the idle was fairly rough when
compared to an E320. I checked several other CLK's and they were identical. We have tried new motor mounts (no fix), but this seems to be common with the CLK V-6.

There is however a software flash for your engine control module
that came out not to long ago. This fixes some quirks in the
ME 2.8 SFI control unit and may be worth investigating.
Give your service advisor a call to see if your car applies.

Good luck.
DR.D