Idle Speed/Throttle Actuator - Electronic: Testing and Inspection

Chart C-2B:

Idle Air Control Circuit:

CIRCUIT DESCRIPTION:

The PCM controls idle rpm with the IAC motor. To increase idle rpm, the PCM retracts the IAC pintle from the seat, allowing more air to pass by the throttle plate. To decrease rpm, it extends the IAC pintle in towards the seat, reducing air flow by the throttle plate. ED22 will read the PCM commands to the IAC motor in counts. The higher the counts, the more air allowed (higher idle). The lower the counts, the less air allowed (lower idle).

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. The Tech 1 is used to extend and retract the IAC valve. Valve movement is verified by an engine speed change.

2. This test checks all wires, connectors, and PCM.

3. This test checks for shorted or open IAC valve coils.

DIAGNOSTIC AIDS:

A slow, unstable idle may be caused by a system problem that cannot be overcome by the IAC.

NOTE: If for some reason the air intake to the engine is restricted the PCM will attempt to compensate by backing out the IAC valve, to maintain desired idle. This may result in IAC count above 60.0. If the engine has another source of air to the intake, the PCM will compensate by extending the IAC - IAC counts may be zero as the PCM tries to maintain desired idle.

1. System lean (High Air/Fuel Ratio) - Idle speed may be too high or too low. Engine speed may vary up and down, disconnecting IAC does not help. May set code EO44. ED07 and/or a Tech 1 will read an oxygen sensor output less than 300.0 mV (0.3 volt). Check for low regulated fuel pressure or water in fuel.

2. System rich (Low Air/Fuel Ratio) - Idle speed too low. ED22 counts usually above 80.0. System obviously rich and may exhibit black smoke exhaust. ED07 and/or a Tech 1 will read an oxygen sensor signal fixed above 800.0 mV (0.8 volt).

Check

- High fuel pressure.
- Injector leaking or sticking.

3. Throttle Body - Remove IAC and inspect bore for foreign material or evidence of IAC motor dragging the bore.