the car - 87 944S
very nasty vibration at idle - and slipping belt (AC belt)
much trouble shooting - new motor mounts, bla bla - many things help a
little, but it still is horrible.  This weekend when attempting to tighten
the tensioner for the AC belt, noticed that the top of the compressor moved.
about 4 hours later I had finally finished replacing the two bolts that hold
the top of the compressor to the mounting bracket - both had sheared off
leaving their threaded portions behind - it's a pain to remove these bolt
fragments without opening the AC system, but I managed (used dental bit in
dremel tool to cut slots for screwdrive in the fragment, then unscrewed).
Now it's a LOT better, but the idle is still rougher than a 87 normal that I
also have here - I've changed the idle control valve, the air flow sensor
(badly worn), ignition wires -it runs fine at higher RPM (like 3000 and
above) - any suggestions?