Diagnostic Aids

Check for any of the following conditions:

• If vehicle is equipped with a rear window defogger, observe the High Electrical Load parameter on scan tool. The scan tool will indicate whether the PCM has received the rear defogger signal. The scan tool should indicate YES when rear defogger is turned on and engine speed should increase slightly. Check for a malfunction in the IAC system if engine speed does not increase.
• A malfunctioning parking light/taillight circuit may cause erratic performance of the electrical load idle-up circuit.
• A PSP switch that is shorted can cause engine idle speed to remain high even when driving straight-ahead.
• A PSP switch that is incorrectly calibrated can cause the engine idle speed to remain low when steering pump hydraulic pressure is high.
• A faulty ground in the PSP switch can cause erratic switch operation. Check that the PSP and bracket are secure and insuring a good path to ground. Inspect PSP switch for a tight installation.
• The scan tool will display A/C Relay Command On when the air conditioning control is turned on, the blower switch is also on, and A/C compressor is operating.
• Observe the IAC Motor Command on scan tool while operating the A/C. The IAC Motor Command percentage should increase 4-12 percent when A/C compressor is engaged. If scan tool indicates that the IAC Duty Cycle is increasing, but the idle quality is unsatisfactory, inspect the IAC system for proper operation.
• If the scan tool indicates that the IAC Motor Command is increasing, but the idle quality is unsatisfactory, inspect the IAC system for proper operation. Refer to IDLE AIR CONTROL SYSTEM DIAGNOSIS .

An intermittent malfunction may be caused by a fault in any one of the idle-up circuits. Inspect the wiring harness and components for an intermittent condition.