I'm back.
After a night or couple hours of sitting, my idle RPMs will oscillate from 800 to ~2000 RPM at startup. After roughly 3 minutes of stop-and-go traffic, the idle issue disappears.
The car is an '89 Jetta (i.e., Digifant II ECU)
My gut is telling me that it's one of the temperature sensors on the front side of the head.
Any suggestions? Check the switches for continuity or resistance? If so, what should the readings be?
TIA! Darryl.