The engine idle speed is controlled by the VCM through the Idle Air Control (IAC) valve mounted on the throttle body. The VCM sends voltage pulses to the IAC motor causing the IAC motor shaft and pintle to move in or out a given distance (number of steps) for each pulse, (called counts). This movement controls air flow around the throttle plate, which in turn, controls engine idle speed, either cold or hot. IAC valve pintle position counts can be seen using a scan tool. Zero counts corresponds to a fully closed passage, while 140 or more counts (depending on the application) corresponds to full flow.
See Figures 1, 2 and 3
- Disengage the IAC electrical connector.
- Using an ohmmeter, measure the resistance between IAC terminals A and B . Next measure the resistance between terminals C and D .
- Verify that the resistance between both sets of IAC terminals is 20-80 ohms. If the resistance is not as specified, the IAC may be faulty.
- Measure the resistance between IAC terminals B and C . Next measure the resistance between terminals A and D .
- Verify that the resistance between both sets of IAC terminals is infinite. If the resistance is not infinite, the IAC may be faulty.
- Also, with a small mirror, inspect IAC air inlet passage and pintle for debris. Clean as necessary, as this can cause IAC malfunction.
REMOVAL & INSTALLATION
See Figures 4 through 11
- Disconnect the negative battery cable.
- Remove the air cleaner assembly or resonator as necessary.
- Unplug the electrical connection.
- Remove the IAC valve. On thread-mounted units, use 1 1 / 4 in. (32mm) wrench and on flange-mounted units, remove the screw assemblies.
- Remove the IAC valve gasket or O-ring and discard it.
- Clean the old gasket material from the surface of the throttle body assembly on the thread mounted valve. On the flange-mounted valve clean the surface to ensure proper O-ring sealing
- If installing a new IAC valve, measure the distance between the tip of the valve pintle and the mounting flange. If the distance is greater than 1.10 inch (28mm), use finger pressure to slowly retract the pintle until the measurement is within specification (refer to the accompanying illustration).
- Install the valve with a new gasket or O-ring. Tighten the thread mounted assembly 13 ft. lbs. (18 Nm) and tighten the flange mounted attaching screws to 28 inch. lbs. (3 Nm).
- Engage the electrical connector to the IAC valve.
- Connect the negative battery cable.
- If removed, install the air cleaner or resonator.
- On 1998-99 models to set the pintle position, turn the ignition key to the ON engine OFF for five seconds. Turn the ignition key to the OFF position for ten seconds, then start the engine and check for proper idle operation.