Thanks for all the suggestions on things to check.

Though I intended to get around to the tune-up on Friday, I ended up just
driving down to San Diego for the weekend.  For the last 3 days, the
engine has idled at startup (sometimes with a little nudge) and
continued to idle when cold and hot as it should.  The last 3 evenings in
southern CA have been a little cooler than before, but not much has
changed otherwise.

So, though I can still check many of the things suggested by all of you,
it remains one of those problems that wouldn't show up if I ever tried
to show it to someone else.  I'm going to get around to the tune-up, but
I thought I'd add some additional data for those of you who've offered
help and might find this info useful for eliminating some of the possible
culprits.  As I said before, it wouldn't idle when cold or hot for the
most part during the last 4 weeks.

Thanks for the help.
david