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 greater than 158°F (70°C).
• Engine running at least 5 seconds.
• BARO greater than 65 kPa.
• Vehicle speed less than 3 MPH.
• IAT greater than -4°F (-20°C).
• Throttle closed.
• Engine speed greater than 175 RPM, higher than desired idle.
• Conditions met for longer than 20 seconds.