I am working on a 2003 s500 with 99000 miles on it. I don't know the history of the car as it came from auction. the vehicle idles smooth and accels smoothly up to 3,000 rpm. either in park/neutral or on the road. but, at approx 3200 rpm there is a shudder type vibration felt throughout the car. it seems harmonic in nature and can come and go. Again, it is there both in park/neutral and on the road. When in park, and held at 3200 rpm, the vibration can be changed, almost eliminated for a few seconds by pressing the c/s switch on the console. Motor mounts, drive shaft joints, etc all look ok. No obvious signs of recent repairs performed