Ehab, I am happy to help in anyway I can as you and Ahmet helped put me on track. I was originally going to reindex the AFM as you and Ahmet described but a friend of mine talked me out of it as I would have been adjusting too many varables with out any benchmark. We only did one change at a time using his car for comparison. My car does not exhibit any hunting at idle at all even when I have adjusted the allen screw but the pitch of the engine and the response were different. The previous owner had adjusted the screw to only 4 turns (rich) from the bottom. My friends allen screw was covered by the plug was stock until we turned it all the way in, about 9 turns to get the benchmark. The hole around my allen screw has a slight shaddow from the position that the screw was at from the factory, when we adjusted the screw 9 turns from bottom we actually went about a turn or so past the shaddow but because his car past the emmissions test who am I to argue, so 9 turns was used. Looking back at the results for the test which showed a slightly high but acceptable NO (Nitrous Oxide) level, I could probly turn the allen screw in about a turn because a slightly High level of NO indicate a slightly lean condition.
This adjustment to the idle mixture and the O2 sensor and the cat made the biggest difference with the emmission test. If you think your cat is still good replacing the O2 sensor is resonable if you get a universal one I beleive $30 for the single wire and $45US for the 3 wire (Bosch 13913) at Pepboys. I replaced the original burntout cat with a CATCO ($79) one that they use on V8 engines. I donn't see any performance problems as my '86 runs just as well as my friends '87 with original cat and O2 sensor.
The original rich condition could be just a bad O2 sensor that you have compensated for by reindexing the AFM. By changing the O2 sensor you may establish new base lines from which you can get back on track.
I know you have an Idle speed problem maybe this page will help you find the source of your problem:
http://porsche-944-garage.tripod.com/shop-manual/fuel-08.htm
Mark
'86 944NA
PS. This may not make a difference but I also replaced my alternator Voltage Regulator/Brush Holder assembly ($23) to ensure that the voltage supply to the DME and all electrical devices were steady.
[This message has been edited by mlue (edited 09-06-2001).]