5kcstq: Continued warm-up trouble

[Wallace White <wallace@remdesign.com>]

I'm still having trouble with the car when it's cold. In the morning,
after an overnight low of ~50 (just a guess), it starts just fine. It
runs just fine for about one minute, and then starts stumbling. It often
dies at this point, unless I modulate the gas pedal just right, and then
it is very difficult to get it to start again. Sometimes it then
backfires. After running for 15 minutes or so (well after the temp gauge
shows plenty of warmth), it has gotten over it and it runs fine.

This happens in the morning (55F, ~8-10 hrs after last running) but not
when I'm driving home from work (70F, ~9 hrs after last running), when
of course it's warmer outside. If I don't drive the car in the morning,
though, it has the same trouble at night or whenever.

This seems like a problem with the "warm-up enrichment" phase of the
CIS, but I don't know what's causing it. At two listers' suggestion, I
checked the fuel pump relay a la Bentley (which doesn't check the relay
itself) and tried the output tests, and everything (including the
frequency valve) clicked when it was supposed to.

Anything else I can try, short of giving in and taking it to my
mechanic? TIA.

- Wallace
  '87 5kcstq 150k