Hi Suginami:

MOTOR MOUNTS:

The car was purchased 2 years ago and did not have this vibration. The vibration developed about 9 month laters. At the one year mark it had the transmission replace and the motor mounts replaced. After the repair, the vibration remained unchanged. So, unless the old mounts failed and the news ones were equally defective from the time of install, they are not the cause.

BAD PLUG, GAP, etc.:

About 3 months ago the car had its 90k mile service including replacing the rotors, caps, plugs, etc. No difference from before to after.

WIRING HARNESS:

During the 90k tune up, the harness would have been removed. One would expect the movement to cause additional stress on the cable, thus more cracking of insulation etc. Thus if there was a slight problem before, it would be even worse afterwards.

But, I won't totally dismiss the wiring harness yet. Called MBZ and gave them the VIN; the are looking up the history to see if it has already been replaced. If not, hopefully they will honor a parts replacement. I'm alittle doubtful; I've had alot work done Mercedes Benz of Bellevue, but they've left me less than satisfied, so I have not been there in about 10 months.

NEXT STEP:

The car is supposed to be ready this evening. I'll take a long test drive and see if there are any changes after this work. If the problem is there, then onto checking a couple such as the vacum hoses and fuel pressure check. If all that checks out, then back to the wiring harness and alittle exploratory surgery.

The tech doing the work seems to know his cars; most importantly he has felt the vibration I'm obssessing on, so at least he knows if the problem has been fixed or not.