V6 stalling

My '95 Audi 90Q has an annoying stalling problem that seems to be getting worse with the cooler weather. The car starts and runs nicely until it starts to warm up. Upon
starting from being cold, it fires off and runs at an idle of around 1000rpm or so, as I would expect. After a minute, or a few minutes depending on just how cold it is, the engine seems to try to drop to the normal 800rpm idle speed but then drops off and will stall half the time. Also, even after the engine is fully warmed, if I let off the gas it may do the same thing. Again, it idles at around 1000rpm for a few seconds to a minute then seems to try to settle back to the slower idle but it stalls instead.
It's been a while since I've cleaned the Idle Stablizer valve but even when I did that before I can't be sure if it had a real effect. I believe the idle switch is working. At least it was the last time I checked it while trying to solve this problem.
Could I be looking for a sensor problem? Temperature sensor, MAP sensor?
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