1999 Chevy Van IDLE AIR CONTROL VALVE

Without a special IAC driver or GM tech II scanner, this is all you can check, other than codes.
10. Remove IAC driver from IAC valve. Using DVOM, measure resistance between IAC valve terminals "A" and "B". See Fig. 7 . Also, measure resistance between IAC valve terminals "C" and "D". If resistance is 40-80 ohms on both measurements, go to next step. If resistance is not 40-80 ohms on both measurements, go to step 22. 11. Using DVOM, measure resistance between IAC valve terminals "B" and "C". See Fig. 7 . Also, measure resistance between IAC valve terminals "A" and "D". If resistance is infinite on both measurements, check for a non-IAC system problem (i.e. vacuum leak, sticking throttle cable, fuel system lean or rich, throttle body, poor electrical connections, faulty PCV valve, A/C compressor circuits). If resistance is not infinite on both measurements, go to step 22. Step 22= replace IAC!