To return to this topic - I finally got around to cleaning the IAC valve last night. Took about 15 minutes and a shot of throttle body cleaner.
The valve looked pretty clean to start with, and I see from my old receipts that it was changed just a couple of months ago, as part of a Ford technician's variation on the "official" Ford moose fix. (the moose is gone, so that worked)
In any case, the car has not stalled since the IAC cleaning, although it still idles a bit low, around 650 RPM.
I might also mention that I went to the dealer with this problem before making my original post, and they found nothing wrong, but charged me $132 (Canadian) for diagnostic work and a re-flash of the ECM.
I'm wondering about the low idle - throttle position sensor?
cheers,