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.
Circuit Description
PCM controls idle speed with an Idle Air Control (IAC) valve to a calculated RPM based on sensor inputs and actual engine RPM. PCM moves IAC valve in or out to vary amount of airflow into intake manifold and thus decrease or increase idle RPM.
PCM commands IAC in counts. A higher count, allows more air to bypass throttle plate (higher idle).
Conditions required to set DTC are:
- No CKP, ECT, IAT, MAF, MAP, TP or VSS sensor DTCs set.
- No EVAP solenoid, EVAP system, fuel trim, fuel injector or EGR pintle position DTCs set.
- BARO greater than 75 kPa
- Ignition voltage 9.5-16.7 volts.
- ECT greater than 122°F (50°C).
- Canister purge duty cycle is above 10 percent.
- Throttle closed.
- Engine speed greater than 180-200 RPM lower than desired idle.
- Listed conditions met for greater than 5 seconds.
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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.