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Intermittent idle speed


Model: 944T, Year:1986, Mileage:160000, Type of use:Street use only
Good Evening,I have one of those wonderfull intermittent problems!! One to the question, the car is a 1986 944 Turbo. The problem is part of the time it idles perfectly, then at the next idle stop could be light to light it will idle slow say 600 rpm and shake/vibrate, the next time it may be fine or idle fast at 1400 rpm but smoothly. I have done almost everything I can think of to fix it. Both ECU's have been checked I have gone through the Porsche electronic testing portion of the shop manual for things like the KLR, TPS, sensors and the like. Also the fuel pressure regulator has been replaced, that helped as it was bad, I have triple checked for vaccuum leaks and it has a fresh tune up. I have missed something any ideas? The car run fines, generates normal boost at the right times per the charts and returns 28 to 30 mpg on long trips. It always starts hot or cold and does not stall. I have had a competent Porsche mechanic check it over also and we are both scratching our head. It has been doing this for a while now and I kind of figured something would break making it easier to find but so far it has been happy motoring. Let me know what you think.Thanks Eric

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