The information is interesting and quite different to my expereience - so in fact I wonder if are all experiencing the same problem. My similar problem happens only when the car is cold, but occassionally after a hard run. I may give the advice of Pirin911 a go this weekend and advise.

Nothing 100% conclusive, but I did want to report some progress...

I replaced the pitted idle air control valve (photo above) with a new one Wednesday, and am happy to report that the off-throttle stalling is 95% reduced. Of the 50 or so times over the past couple of days when conditions were right for stalling, it has done so only a couple of times.

With the A/C off, it now behaves as it should during throttle-off, dropping to about 800 RPM, and staying there without a fuss. With the A/C on, during throttle off, the engine still has a tendency to drop way down to 100-200 RPMs, before bouncing back to 800 RPM and staying there. And a couple of times it has hit zero and stalled.

So, the new valve has helped matters significantly, but there is still an idle recovery problem somewhere.

I plan to:

1. Check again for intake leaks.
2. Adjust the idle air/fuel mix.
3. Replace the ECU regulator.

I will start a new thread when I have conclusively identified all of the causes and fixes.

This is startlingly similar to what I've experienced on my 86 over this summer. I am no longer experiencing the stalling and I am not sure why. It is to the point now where it is good enough to take to a real wrench for fine tuning. The major things I have done to address the situation

checked for unmetered air leaks - none found [yet]
cleaned the ISV [but didn't take it apart yet]
adjusted the idle speed multiple times
adjusted the idle mix [unscientifically]
chipped the car [Steve Wong]
tested the idle switch
tsted the full thrttle switch [while I was in there]

then,

I set the DME to lean out the overall mix [position 3] and it stopped the stalling/bouncing from 100 rpm type behavior!

I didn't want to leave it at this, so I thought I would try leaning out the mix by 'adjusting' the spring in the airflow meter and returning the DME to normal. I tightened the spring by three notches and it is fine now. I may mess around with it some more, but for now, it doesn't stall and I can drive it again. I'm not knowledgeable enough to say this should affect the root problem or if it is just impacting some symptom.

Randal,

Greeting from another Ahwatuke... er Ahwatukean... Ahwatuker... um, neighbor.

Glad things are looking up with the idle problem. Check out this post that outlines checking the idle switch. There's more to check than just the click! As you can see by the post our other neighbor, Jeff, can really come in handy sometimes.

http://forums.pelicanparts.com/porsche-911-technical-forum/112494-news-flash-fellow-pelican-solves-hanging-idle-mystery.html

You're welcome to try my spare DME relay if you haven't tried that yet.

I am definitely noticing a correlation as you have, CrossT, between the stalling and the idle air/fuel mix. Leaning it definitely alleviates the problem. I had leaned it at the same time I replaced the valve, and I thought it was mostly the valve that fixed things. WRONG (though it didn't hurt). I put the idle mix back to where it was, and the stalling was back. Yesterday, I leaned it down further than last week. Today was really hot, and it never stalled. I'm going to drive a several more days as is just to be sure.
LeeH, on the idle switch, I did electrically verify that the contacts were opening and closing properly. Thanks for the offer. I may take you up on it if I continue to have problems.