Steve, thanks for the quick answer.
I didn't know that with the electric plug off the idle valve a car would run at about 50rpms greater than usual. This was an important thing to know for correctly adjusting the idle valve.
Below is my understanding of the air valve's operations.
The air control valve stays partially open when disconnected and with a little current it fully closes the air passage. Then, with even more current it partially opens again, and at full 12 volts it open up widely. In the picture below you can see how it happens. The red mark is what blocks the air inside the valve. It move to the left as more voltage is applied. I think the real idle control should be happening at the stage 3 in the picture below.
The screw on the side of it should regulate the amount of air passing through it when it is disconnected.
Can you explain the difference between a carb cleaner and injector cleaner and if the second one can be used for cleaning the valve?
1989 230E, 8v, 166.000 km, updated to 94/95 trunk & hood
2002 Daewoo Nexia 50.000 km
1987 VW Jetta GLE 16V, Recaro seats
1982 Volvo 240 DL (lovely car!)
and few more american cars.