I have a '93 960 (who lived through a timing belt brake) which has a problem for the past few months that a service shop can't find. When driving at around 45 MPH and the automatic transmission adjusts itself to around 1500 RPM, the engine starts hesitating, as if it wants to stall. Sometimes it is worse than other times. When I switch to a lower gear or gas it, the problem seems to subside/disappear. The tachometer does not fluctuate when this happens. This usually happens when the engine is warm, but most times a few miles after I first start out in the morning (temperature gage reads that the engine is warmed up at that time).

I brought the car a few times to the service shop and unfortunately it is an intermittant problem and the service shop can't figure out what to look for. They did the usual things such as look for trouble codes, check ignition system (they did say the plugs were worn and replaced them), fuel flow, etc.. They indicated that the engine has heavy carbon deposits and that should be cleaned out (e.g., fuel injection & air induction service).

Any ideas?

Alex