IAC Valve Circuit CIRCUIT DESCRIPTION The IAC valve is situated on the intake chamber. Intake air bypassing the throttle valve is directed to the IAC valve through a passage. A step motor is built into the IAC valve. It consists of 4 coils, a magnetic rotor, valve shaft and valve. When current flows to the coils due to signals from the ECM, the rotor turns and moves the valve shaft forward or backward, changing the clearance between the valve and the valve seat. In this way the intake air volume bypassing the throttle valve is regulated, controlling the engine speed. There are 125 possible positions to which the valve can be opened. Throttle Body Air Flow Meter Intake Air Chamber Valve Coils Rotor Valve Shaft FI6511 Reference INSPECTION USING OSCILLOSCOPE A/C Switch OFF → ON (IAC Valve open) ISC1 ISC2 20 V/Div. ISC3 ISC4 10 msec./Division • With the engine idling measure wave forms between terminals ISC1, ISC2, ISC3, ISC4 and E01 of engine control module when A/C switch ON or OFF. HINT: The correct waveforms are as shown. A/C Switch ON → OFF (IAC Valve close) ISC1 ISC2 20 V/Div. ISC3 ISC4 10 msec./Division FI6538 FI6537