For a variety of reasons, I couldn't test the car until today. It has
not been driven at all since then (two weeks), but when I got ready to
test it today, here's what I got:

1. The car fired right up.
2. I let the engine warm up for about 5 minutes.
3. Then I drove around the block four or five times.
4. Then I took it up to 50mph for a couple of minutes.
5. When I dropped the speed to under 5mph, the car died.
6. After waiting less than 15 seconds, I started the car again with no
problem.
7. I repeated steps 2-4 again and again, but the car never died on me
again.

The only thing I did notice was that at one point, when the car was
idling, a little bit of burnt-oil smelling smoke came out of the vent.
There was no smoke when I opened up the hood, but there was kind of a
lingering burnt-oil smell. I don't know if that is in any way related
to my problems, but I just can't figure out why the car would only
intermittently stop working.