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951 Intermittent very poor throttle response

Fuel System

Vehicle Information: Model(924/944/968): 951; Year: 1995; Body Type: Coupe; Total Mileage: 81,xxx;

After running excellently with the Automotion chipset, the car has developed periodic throttle response problems. When it acts up, the throttle response is almost reversed. It will barely idle, often stalls coming off the throttle, but most irritating is that I can barely raise the revs to take off. Pressing the throttle results in a drop of rpm and a lot of stumbling. After nursing the throttle for 5-10 seconds, I can get enough revs to roll forward. Then, it is very weak and rough running. It is a fearful experience just to try to get across a busy intersection. Freeways are out of the question.It has been to the local Porsche dealer twice. The O2 sensor was changed. They could get it back to running OK. But the WOT overboost mode still so bad that, when running "normally" I don't even give full throttle. I also noted that WOT mode seems to result in a lot of grey? (not black or white) smoke.It has been a daily commute car for over two years, and it had been almost scary strong. Hence, the interent power is probably the only thing that has allowed me to limp it to the dealer twice. They gouge me for about $1k each time without really finding the issue.BTW, the week before the latest throttle problem came back (happening about every 6 months), the car poured white smoke for about a minute after cold start. That was 3 out of 4 days. But that has stopped. During this latest event, the problem persisted when I started it the next morning. The next time I started the car, it seemed OK and I drove it to work without incident. On the drive home, it was OK for about half of the 45 minute city street commute. Then it acted up, such that I could barely move it through a couple of lights. Then it was OK the rest of the way home???The car uses a quart of Mobil One every tank and a half.I am the original and current owner. If I can get it running reliably, I'd like to put it back into commute service (even though I only get about 16-17 mpg). Maybe I should break down and start driving my '2002 C4S daily (it only has 9K miles).

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