With the electric plug off the valve stays at an openning that would run a car about 50rpms greater than would be had if the idle was controlled normally in neutral with the airconditioning off. If this were the case the A/C would then drop the speed (at the fixed volume) to below normal speed and then when put in gear it would be real low.
You need to think of the volume of air needed. If you shove a cork into the valve and drill a 4mm hole in it the engine should run at a little faster than the valve unpowered. (Maybe it was 5mm). That is the size of the openning and a way to verify the proper outside air intake. If you stick this cork in it then it better run at less than 900 or you have air coming in somewhere. Air equals engine speed.
Bosch Master, ASE Master, L1
33 years MB technician