I have a 1991 300E 2.6 W124. It has a problem wherein the motor will rev then back-off, all by itself. This continues for a while then it behaves normally. After a while it starts misbehaving again. It can happen when the engine is cold or hot. Cruise-control really gets confused while it does this automatic accelerating, which makes the car drive jerky. I have taken the car to Worrells, who claim to be the most experienced MB dealer/maintenance in Melbourne (Australia) and they are stumped. They have had the car for a week and don't want to give it back until they can identify and fix the problem. Can anyone please help?