Idle Speed/Throttle Actuator - Electronic: Testing and Inspection

Chart C-2C Idle Air Control:

CHART C-2C

IDLE AIR CONTROL

2.0L "J" SERIES

FUEL INJECTION (TBI)

Idle Air Control Connector Schematic:

The ECM controls engine idle speed by moving the IAC valve, to control air flow around the throttle plate. It does this by sending voltage pulses (called "counts" or "steps") to the proper motor winding. The motor shaft and valve move a given distance for each pulse received.
a. To increase idle speed - ECM sends enough counts to retract the IAC valve and allow more air to flow, until idle speed reaches the proper RPM. This increases the ECM counts.
b. To decrease idle speed - ECM sends enough counts to extend the IAC valve and reduce air flow. This will reduce the ECM counts.
The ECM "learns" the correct valve position to maintain proper idle RPM. If the "learned" IAC valve position is incorrect, the ECM will command a reset. The reset will occur after the next engine start and vehicle speed is greater than 35 to 45 MPH.

1. Be sure to disconnect the IAC valve prior to this test. The test light will confirm the ECM signals by a steady or lashing light.
2. Before replacing an ECM, be sure to check the resistance at the IAC motor windings. Failure to do so may result in a repeat ECM failure.
3. Diagnostic Aids:

a. Park/Neutral Switch (Automatic Transmission Only) - If the ECM thinks the car is always in neutral, idle speed will not be correct in drive range, Chart C-1A.
b. A leaking injector will cause poor idle quality due to excess fuel.
c. A sticking injector causing a too lean or too rich condition can cause a poor idle condition. A code 44 or 45 may be stored.
d. A sticking throttle shaft or binding linkage causes a high TPS voltage (open throttle indication). The ECM does not recognize a closed throttle and will not control idle. Monitor TPS voltage. Voltage should read less than 1.2 volts with throttle closed.
e. EGR "on" while idling will cause roughness, stoppage and hard starting. Chart C-7A.
f. Battery cables and ground straps should be clean and secure. Erratic voltage will cause IAC to change its position resulting in poor idle quality.
g. Power Steering - Chart C-1E. ECM should compensate for Power Steering loads. Loss of this signal would be most noticeable when parking and steering loads are high.
h. IAC valve will not move if system voltage is below 9 or greater than 17.8 volts.
i. MAP - An erratic sensor output can cause and unstable idle condition.