Hitachi Idle Air Control (IAC) Valve Assembly With Vent/Filter
The Idle Air Control (IAC) valve assembly (Figure 117) and (Figure 118) controls engine idle speed and provides a dashpot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The PCM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning the IAC valve to control the amount of bypassed air. The PCM monitors engine rpm and increases or decreases the IAC duty cycle in order to achieve the desired rpm.
Hitachi Idle Air Control (IAC) Valve Assembly With Air-Assist Injectors
On applications with air-assisted injectors, the IAC valve (Figure 119) also supplies a small amount of air into the path of the fuel injectors. The jet of air causes an increase in fuel atomization at low speed and light load conditions.
NOTE : The IAC Valve Assembly is NOT ADJUSTABLE and CANNOT BE CLEANED.
The IAC valve (part of throttle body assembly) has an internal diode on some applications. If the internal diode is measured in crossed terminal position with a digital multimeter, there will be an incorrect or negative reading. It is important that the mating component and harness connectors correctly oriented. Diagnostic procedures emphasize this importance.
The PCM uses the IAC valve assembly to control:
No touch start
Cold engine fast idle for rapid warm-up
Idle (corrects for engine load)
Stumble or stalling on deceleration (provides a dashpot function)