UPDATE:
Apparently the problems were moisture related, since all the strange gremlins happened during snow, sleet and rain.
I just drove another 300 miles (Fayetteville to Asheville, NC) without any problems (dry & sunny skies).
Something came back after 10 months thought, the oscillating idle (600 to 1100 RPM). With an occasional sticking at 1100 RPM.
Engine bay is very dirty with road salt. I will try to clean the idle control valve next weekend (this fixed the oscillating idle before), remove the potentiometer and evaluate it.
May be is time for a new pot, unfortunately I did not remember to check the duty cycle as the problem was actually occurring.
That would have pinpointed the problem in "real" time.
Will update.

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1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
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