Toyota 22270-0A040 Valve Assembly, Idle Speed Control

First of all, the engine idle speed is controlled by the Idle Control Valve, which regulates the airflow bypassing the throttle plate into the intake manifold. The IAC valve is controlled by the PCM and adjusts the air intake based on engine demands and operating conditions. To check the IAC valve, apply the parking brake, shift the transaxle to Neutral or Park (automatic), and block the drive wheels. Install a tachometer and start the engine, comparing the idle speed to specifications. If the engine speed changes, the IAC valve is functioning properly; then, measure the IAC valve resistance and if the resistance does not meet specifications, replace the IAC valve. If it does, further investigate the wiring or PCM. If the IAC operates correctly, inspect the wiring harness since the PCM may be defective and should be checked. For replacement, remove the throttle body, detach the IAC valve and gasket, and reinstall using a new gasket.

This procedure applies to the models of 2003 and earlier only. This is set at the factory and cannot normally be adjusted; however if the throttle body has been replaced or if there are suspicions that the minimum idle speed has been changed, then the vehicle should be taken to a dealer service department or taken to any automotive repair shop. On these models, the Idle Control Valve (ICV) is used in the determination of the engine idle speed by allowing air to by-pass the throttle plate into the intake manifold in accordance with signals from the PCM when the latter deems it necessary due to changing demands or conditions of the engine. To check the idle speed, the parking brakes must be set, the lever of transaxle shifted to Neutral or Park, the wheels should be blocked, and a tachometer must be connected. After this, engage the engine and let it warm up to normal idling speed and then measure the idle speed. Connect the terminals of the diagnostic test connector for the model year by employing a jumper wire. Typically, the engine speed should rise to about 900 or 1000 rpm for five seconds then goes back to the idle speed. In this case, if the engine speed changes as required, the ICV is working correctly; else, measure the ICV resistance, then, disconnect the valve electrical connector and check the resistance between the center terminal and each end terminal with an ohmmeter, against the fitted resistance. If the resistance is not as specified, the ICV needs to be replaced; if it is the same as specified then there may be a problem with the wiring or PCM. To diagnose further, remove the ICV and connect the battery to the valve connector where grounding the outer terminal will cause the valve to open and close. If everything with the ICV is fine, check the wiring from the PCM to the valve; if wiring is okay then the PCM may not be fine and should be tested by a dealer. For replacement, unbolt the throttle body and then unplug and remove the ICV and its gasket by the two screws that are situated below the throttle body, then give way by installing an all-new ICV gasket before bolting the valve in the reversed sequence.

The engine idle speed is controlled by the Idle Air Control (IAC) valve.