I read you replaced the Idle Control Valve with an used one.
Have you tried to clean it?
I was experiencing the same problem, after cleaning the ICV the problem never came back.
Lots of carb cleaner, and then some WD-40 for lubrication.

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