Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1998METRO L4-079 1.3L VIN 2 MFIREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSDESCRIPTION AND OPERATIONPOWERTRAIN CONTROL MODULE FUNCTIONPCM OUTPUTS DESCRIPTIONIDLE AIR CONTROL (IAC) VALVE
1998 Chevrolet Metro L4-079 1.3L VIN 2 MFI
Idle Air Control (IAC) Valve
1998 Chevrolet Metro L4-079 1.3L VIN 2 MFISECTION Idle Air Control (IAC) Valve
The idle air control (IAC) valve is attached to the underside of the throttle body. The powertrain control module (PCM) uses the IAC valve in order to control engine idle speed. The PCM controls the IAC valve by varying the ON time of a repeating ON/OFF signal (duty cycle). A magnet inside the IAC valve operates a rotary valve that controls the opening of the idle air (bypass) passage in the throttle body. The idle air passage allows air to enter the engine without passing over the throttle valve. The strength of the magnet in the throttle body is concurrent with the current flow in the IAC circuit.
The IAC valve contains an engine coolant passage that enables the IAC valve to operate more efficiently at cold temperatures. The IAC valve enables the PCM to easily control engine idle speed by precisely metering the engine's air intake at closed throttle.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.