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rough idling and stalling 964

Old 03-30-2008, 09:36 PM
Thread Starter
Join Date: Aug 2007
Posts: 15
Default rough idling and stalling 964

After I had the computer checked out on my 1990 911 C 4, the car was running fine, but after a while the car did the same rough idling and stalling before the computer check. I tried to have the problem solved by good mechanics around my town, but nobody seems to know the problem and the next dealership is 200 mls. away and they have nobody to work on aircooled cars anymore. The fuel pump relaygoes on and off in the DME relay and in the engine compartment at the same time a relay goes on/off as well (solonoid valve). My diagnostic software shows a fault at the throttle position switch. Is there a connection from the switch via control unit to the fuel pump? And if I have to change this switch, where can I find a new one? I only come across one to the year 89 and from 95. Any help is very much appreciated.
Old 03-31-2008, 11:59 AM
Join Date: Sep 2007
Posts: 611
Default RE: rough idling and stalling 964

I think you need to throw yourself on the mercy of Porsche Doc for a hint of where to go next.
Just a thought how is the MAF sensor? Perhaps try cleaning it with some specialised cleaner I've seen advertised in the US but not been able to locate in the UK.
Regards Big Bob
Old 03-31-2008, 04:13 PM
Thread Starter
Join Date: Aug 2007
Posts: 15
Default RE: rough idling and stalling 964

Thanks a lot Bob. I have taken out the MAF and tested and cleaned it. The test wasfrom approx. 300mV closed to approx. 6-7 V fully open, and the plate moves free and easy. I took out the 2 throttle switches, they work on/off, because these are microswitches. I checked out the ignition system (all replaced, when engine was rebuild 12.000 mls. ago). Car starts in 2 sec. and runs approx. 15 min. perfect, if I start the engine again after a pause of approx. 5 min., the engine has a problem running and idling is very erratic and after a few sec. it stops, because the fuel pump relay shuts off/on the fuel supply for seconds. I opened the DME relay, to see which relay it is, the power supply to the DME is perfect, but the fuel pump relay goes on and off. DME and fuel pump is new and fuel pressure is correct. I am thinking to take the car apart and sellin pieces, if I can't solve the problem, but I hate it, after spending $ 40.000 on restauration making the car like showroom condition.

1990 Porsche conv.C 4, 1969 Jaguar XKE roadster, 1961 Morgan roadster, 1968 Mercedes 250 SL, 1956 Ford Thunderbird
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