Diagnosis Please.. Rough running question
 

Here is the short version: 86 944 N/A, 113000 miles. Idles extremely rough and misses at all rpm’s until it reaches full temp. Started one day, meaning it did not gradually get worse, it had always been fine and then… Here is what I’ve done so far; both motor mounts, O2 sensor, temp sensor, one suspected fuel injector, new plugs.. I’ve checked for vacuum leaks, vacuum at both fuel pressure regulators and the air flow meter looked alright ( don’t really know what I’m looking at though). A local Porsche repair shop after 2 days and several hundred dollars said “we don’t know”. They replaced a plug wire and ran several diagnostics and system checks. They thought it might be a broken valve spring? Someone else thinks it maybe the idle stabilizer valve. Any ideas would be greatly appreciated .. This is getting frustrating…

Thanks ..

You mave have the same problem that I have been investigating on my '86na. My na '86 starts great and no flooding on start up, hits and starts right up fine. Then in a couple seconds it gets really rich and chugs and puffs black smoke for about 30 seconds and then clears up and runs fine. The colder the worse it is. Does this match your problem or does your's have to totally warm up before it clears up?

My guesses would be (in the order of likeliness):

Vacuum leak (it COULD be head gasket, but I doubt that, did you check compression/leak down)?

Idle stabilizer valve,

And (sorry to say) DME...

Anyway, if the shop cannot tell you for sure if your idle stabilizer valve is NOT at least a part of the problem, after you spend 100s of $, then you need to start going to a different shop...
Ahmet

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It's all the driver...

Hook a vacuum gauge up to it at idle you should have a steady reading of 15" to 22" Hg. If it has good vacuum spray propane or carbuator cleaner into the intake and see if it the engine smooths out if so check for vacuum leaks by spraying carbuator cleaner on vacuum lines fittings and intake seals. If you can't find any ohm the injectors. Also do a compression check. Get a spark tester and check for spark at the end of the plug wires. If it is a broken valve spring you should find it with a vacuum gauge.