1991 940 GLE, When I start the idle sets at 1050 rpm, but after 15-20 seconds it"ll climb to about 1800rpm and won't drop. I've checked for vacuum leaks and found none, unplugged and checked all wiring connectors, found no corrosion on any plugs, good fuel pressure, plugs are burning clean - none are fouling or white or oily dark, tps is reading .5 volts, is this the correct reading? Help please

 

Idle Air Control valve.

 

Hey thanks Cbevis, Pulled the iacv and washed down with throttle body cleaner, allowed to dry and reinstalled. Started car and same issue continues. Repulled valve and had my son turn the ignition on and saw the valve move but not rotate more than a 1/8 inch. Is the valve supposed to continue rotating or just move a small amount? After I reinstalled I fired the motor and allowed it to idle for 25 minutes but the idle remains at 1800 rpm. Any more suggestions out their?