Have very similar sounding problem with 93 300 E 3.2 134,000. When I showed the thread to my better half, she said "that's our car!" Interestingly ours is a 124 chassis. The vibration starts at about 35 and stays until 60 MPH under light throttle pressure. It is felt mostly in the drivers seat and is at a high frequency. Cannot be felt in the steering wheel at all.

It almost feels like lock-up torque converter chatter.

Benz master tech used car for a couple of days and says it is not normal but cannot pinpoint the source. Local trans shop says they do not think it is the trans.

Replaced tires(they were due), motor mounts (at first this seemed to correct the problem), trans mount, both flex discs, rebuilt driveshaft, plugs and wires , one coil (looked old, others had been replaced), compression test OK.

Local vo-tech teacher drove it and thinks it may be an injector problem, this was without him knowing that it probably has a bad injection wire harness. Now the thought is what about an injector spraying at the wrong time due to a false signal as a result of a short? No check engine light or codes stored.

If problem is found I'll post a reply but the above is what hasn't fixed it, and this vibration is really annoying.

Two other pieces of info., the differential bushings are sloppy and the vibration does not change if you apply the parking brake. Has become slightly worse over last 13K miles.

Thanks in advance to all.