First of all congratulations on your helpfull posts!
I recently bought a 1990 Guards Red964 C4. Theengine had oil leaks and was repaired September2003 with 99,5 K miles. At the time the clutch was also replaced as was the oil cooler line.The repairs were done by HBL Porsche in Tysons Corner VA.Then the car was sold and the owner put only another 3k miles in the next 4 years, fortunatelly the car was garaged and is cosmetically in very good shape. Last August I bought it with 103 K milesand had HBL Porsche adjust the valves, replace the brake fluid and the sparkplugs. Theengine now seems to be more responsivebut there is still a non-stable idling varying between 750 to 850 RPM. Also whenI accelerate from idling there isa small lag in response. Above 1000 rpm it works better but I have the feeling that the engine could be more responsive. HBL told me thatI would probablyneed a newdistributor in order to correct the problem but they did not guarrantee that it would solve the problem.Do you think I should go ahead or try other possibilities?A couple of days ago I tried a can of BG 44K andit improve somewhat the responseabove 1000 RPM , but the idling variationis still there. Best Regards , Ed.

 

There are a couple of things that could be of issue. One is the AFM, the tracks on the armature may be getting worn out. Another thing I would do is check the idle stabilizer valve and have them make sure that is functioning. Lastly I would look at the distributor, as it is going to be the most expensive.