My 964 is a 1991 with 93,000 miles on it and runs great (normally). However, it would be purring along fine when all of a sudden the engine would start sputtering and just about all the engine check lights would begin randomly flashing. I'd pull over and let the car idle for a few seconds and the condition would just go away like nothing happened or I'd shut down the engine and re-start and the condition would sometimes go away. This condition is intermittent and sometimes would not re-appear for 200-300 miles. Also the radio would completely go off and on prior to this happening with sound distortion heard over the speakers. (this may be totally unrelated but always precipitates the event). I had the fault codes read out and found nothing unusual. I ran my car with a voltmeter attached to the cigarette lighter socket and found output of between 13.65 and 13.75 volts when the car was running normally. But just recently the car has been acting up again, (warning lights, unstable idle rpm (1,100 - 700 rpm), engine check lights, radio cutting in/out with distortion heard over the speakers) and this time I noticed the voltage "dancing around" with output between 13.3 and 14.2 volts. Some further background, this problem happened before and after I had new plugs/valve adjustment as well as a new ignition switch (electrical portion only) installed .? Anyone diagnose a similiar problem? Thanks

 

Dear Ron,
From your description of the fault I suggest you get the alternator/regulator out and rebuilt. I think the regulator brushes have had the gong and you are getting spiked. Positive and negative versions thereof.
DME for one does not like getting spiked and a loss of voltage will shut it down real quick as will too high voltage. Hence you stall and get the engine check light flashing.
The distortion in the speakers will also be caused by the fluctuating voltage. Your voltmeter readings are enough evidence I would need to be looking very closely at the alternator. Maybe check all the connections at the alternator first. Chaffed/damaged wires, especially the blue wire at the alternator or through the loom are not uncommon,
Ciao,
Adrian
911C4

 

Hey Ron,

Another thing to check is the spark plug wires and the spark plug boots. I had a similar set of symptoms (very intermittent) when I first bought my car, and it turned out that one of the spark plug boots was cracked.

You might also check the ground strap on the hinge of the engine cover. There was a tech bulletin that recommended moving it onto the side of the hinge so it didn't come into contact with the coil wire.

Good luck!

-- Melissa