Strange 5KCS Stalling/Hard Start

[Steve Sherman <spsherm@ibm.net>]

My wife's 86 5KCSTQW is having an unusual stalling and/or hard start
problem.  It goes like this...

Most of the time it starts and idles just fine.  Usually starts in < 1
sec and idles at 800-900rpm very steadily.  Every so often (was once
every month or two, now more like twice to 3x a week) it will go into a
"strange mode" where it will have no power, idle at 200 rpm very roughly
and stall, and be very hard or impossible to restart.  If it was running
when this happens it usually is hard to start immediately after the
stall.  Occassionaly it will be hard to start right from the get-go.

I've noticed that if I rev the engine up to 3000rpm for a few seconds it
seems to cure the problem.  Likewise when in hard starting mode,
cranking with the accel pedal floored and letting it rev up usually
helps.

Any guesses as to what this may be?  I've checked for vacuum leaks and
did not find any obvious ones (pulling the dip stick does effect idle
speed a bit, so I am discounting any major vacuum leaks)  Ignition cap
wires rotor and even the distributor are fairly recent and all seem OK.

I am scratching my head as to what else to look for.  Any ideas or leads
would be appreciated...

TIA

Steve