V6 12v stalling at idle

[Gene Caldwell <optic@halcyon.com>]

I first noticed this last summer while moving slowly in traffic on a hot
day.  The engine was not idling as smoothly as normal, then the idle
speed dipped to about 200-300 rpm and then it just stopped.  It will
start right back up as if nothing was wrong.  This has been a rare event
until lately.  Now it's beginning to do it a lot.  If I hold the engine
speed about 1000 rpm (off the idle stop) it will run fine.  It seems to
only do this after the engine is warmed up.  Fuel consumption is
normal.  Car is '94 90.  Any insights greatly appreciated.

-Gene