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 by-pass 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, EGR flow or EGR pintle position DTCs set.
- ECT and IAT greater than - 40°F (- 40°C).
- Engine running at least 5 seconds.
- BARO greater than 65 kPa - except VIN 1.
- BARO greater than 70 kPa 0 - VIN 1.
- Vehicle speed less than 3 MPH.
- Throttle closed.
- Engine speed greater than 175 RPM, higher than desired idle.
- Conditions met for longer than 20 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.