89 911 bucks when warm on light throttle

[89Carrera]

My 89 Carrera bucks when warm. It feels like the engine is cutting out or running on less than 6 cylinders. The problem exists only when coasting on a light throttle. There is no hint of a problem when the car is accelerating. Oddly enough the problem also disappears at exactly 2000 rpm. The problem occurs above or below 2000rpm. I have owned the car for 10 years, it now has 96k miles and has been well maintained. I have spent a bunch of money at some great Porsche shops and none have been able to fix.

Any suggestions? Work done so far:

Replaced: injectors, DME relay, cams reset, valves adj, spark plugs, ignition wires, distributor cap & rotter

Tested (parts swapped): Ignition coil, air flow meter, temp sensor, motronic control unit, air box

Other Tests: compression test (160-175), fuel pressure, engine vacuum leak, injection and top end fuel system clean, engine "leak down" test (all cylinders are 2-3%), cylinder head temp, exhaust cylinder temp (1 cylinder runs cooler?), exhaust back pressure, exhaust analyzer indicates lean mix below 2000rpm, heat exchanger, battery, DME pickups, air flow meter, altitude sensor

[Loren]

As I recall the usual causes are a bad cylinder head temperature sensor or a bad O2 sensor. Either way the cars computer reads the engine temperature so that it can adjust the fuel mixture as it warms up. It also looks at the O2 sensor readings to make fuel adjustments.

[89Carrera]

As I recall the usual causes are a bad cylinder head temperature sensor or a bad O2 sensor. Either way the cars computer reads the engine temperature so that it can adjust the fuel mixture as it warms up. It also looks at the O2 sensor readings to make fuel adjustments.

Thanks for the reply........we tried new parts for both and it made no difference......

[magcuda]

any clutch work before this popped up? possible flywheel teeth damage

[89Carrera]

any clutch work before this popped up? possible flywheel teeth damage

........clutch was replaced some time ago and before the problem started.........flywheel is an interesting thought although I think the fact that the engine has the same symptoms when the car is stopped with the engine running on idle probably indicates this is not the prob.......tell me more if I missed the point....and thanks for the suggestion.

[magcuda]

the flywheel teth passing by the speed and reference sensor makes an AC voltage that tells the DME rpm and tdc location. a damaged tdc pin will cause a lower voltage = running problem.

also check the ground strap from the front of the tranny to the body

[stlrj]

, exhaust analyzer indicates lean mix below 2000rpm

Was the analyzer probe inserted inside the tailpipe? Does your car still have a cat?

Joe