Adjust Idling

[FMO]

Hi!

I am trying to adjust the idling on my 1985 Porsche 911 3,2 Carrera.
If I keep the terminal B & C bridge, the idle is complitely steady at approx 840 rpm. Once I take it out , it begin to be more unstable , approx 800-850 rpm.

Anyone knows what the failure can be?

Best regards
FMO

[VMAX1]

Idle control valve? Search idle control valve and you will probably find a bazillion posts. That would be a start.