Idle Control Valve / Stepper Motor
1. What is the idle control valve / stepper motor and what is its function in the car?
The idle speed control (ISC) valve, also called the idle air control (IAC) valve, is used in fuel-injected engines to control idle speed. The stepper motor, a type of idle valve, consists of a pintle that blocks or allows air to bypass the throttle plate. The powertrain control module (PCM) regulates the operation of the stepper motor.
2. What are the symptoms of a faulty IAC / stepper motor?
Unsurprisingly, a faulty IAC often results in engine idle problems. An engine idling too fast or too slow may indicate a defective IAC. An engine that stalls can also indicate IAC issues.
3. How can I check if my IAC / stepper motor is faulty?
Most of the time, if there is a problem with the IAC or its control circuit, the PCM will set a diagnostic trouble code (DTC) and illuminate the “Check Engine” light (CEL). If the light is on, you can connect a diagnostic tool to the designated port under the dashboard and read the listed error codes. If the code indicates a problem with the IAC or its circuits, the vehicle-specific repair manual should be consulted before proceeding with further tests.
4. How do I change the IAC / stepper motor in my car?
The method for replacing the IAC varies from vehicle to vehicle, but it is fairly straightforward in most cases. Specific repair information should be consulted before you replace your IAC. A typical IAC replacement proceeds as follows:
Disconnect the negative battery terminal
Disconnect the IAC electrical connector
Remove the IAC valve mounting screws
Remove the IAC assembly
Reinstall in the reverse order of disassembly
Idle Control Valve / Stepper Motor IAC
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