My '93 944T with 100K miles still gives me fits. There is still a noticeable shudder when idling, and the idle RPMs seem to vary between 500 and 800 RPMs. So far, I have done the following: 1) Cleaned the throttle body. 2) Cleaned the IAC valve. 3) Replaced the plugs, distributor cap, and rotor. 4) Replaced plug and coil wires. FWIW, I have also just replaced the timing belt, tensioner and front seals. The idle shudder improved slightly with the new wires but has not disappeared. Now that warmer weather is here, I have been driving with the AC on and I notice that when the compressor kicks in, the car shudders quite a bit, especially while in idle, almost to the point of the engine dying. The whole car shakes (you can really feel it in the driver's side door). The mechanic who did the timing belt didn't think that there is a vacuum leak. Any other ideas? Thanks.
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Steve Van Steenhuyse ('95 944T, 97K)