Thanks all!  Here is a quick summary of the suggestions for my cold
idle problem, and how many people "voted" on each:

1. Temp Sensor II (2 votes)
2. Vacuum leak (2 votes)
3. Valve adjustment (1 vote)
4. Electrical connection or grounds (3 votes)
5. O2 sensor (1 vote)
6. Aux Air Valve (1 vote)
7. Air, fuel filter (1 vote)

More info:  around the time this happened, I thought my engine was
dead and was shopping for a new one, as no amount of fiddling would
keep it running.   Eventually, I discovered that the previous
mechanic had not tightened the throttle body bolts to the intake
manifold (leading to a massive, intermittent vacuum leak).  Before I
had figured this out, however, I replaced cap plugs & rotor, adjusted
the valves, changed the O2 sensor, AFM, and set the timing.    So
it's quite possible that one of the things I "fixed" actually caused
the problem.

Ok, off for more diagnostics!  Thanks again for the suggestions :-)