Diagnostic Aids

Perform this test when instructed during QUICK TEST or other test step. This test is only intended to diagnose the following:

• Idle Air Control (IAC) valve.
• Idle Speed Control (ISC) valve.
• IAC, ISC and VPWR harness circuits.
• PCM.

1. 1) IAC Valve Resistance
   
   Disconnect Idle Air Control (IAC) valve harness connector. Measure resistance between IAC valve terminals. If resistance is about 10 ohms at 77°F (25°C), go to next step. If resistance is not about 10 ohms at 77°F (25°C), replace IAC valve.
2. 2) Check Power Supply
   
   Turn ignition on. Measure voltage between ground and IAC valve ignition power circuit at IAC valve harness connector. If voltage is greater than 10 volts, go to next step. If voltage is not greater than 10 volts, repair open in circuit.
3. 3) Check IAC Valve Circuit
   
   Turn ignition off. Disconnect PCM and IAC valve harness connectors. Inspect harness connectors for damage. Measure resistance of IAC valve circuit between PCM harness connector and IAC valve connector. See CIRCUIT PIN IDENTIFICATION  table. Resistance should be less than 5 ohms. Measure resistance of IAC valve circuit between PCM harness connector and ground. Resistance should be greater than 10 k/ohms. If resistance measurements are as specified, go to next step. If either resistance measurement is not as specified, repair open or short to ground in IAC valve circuit.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 3)  to step 10)  . No test procedures have been omitted.
4. 10) Check IAC Valve
   
   Apply power and ground to IAC valve terminals. See Fig 1. If a click is heard when applying battery power to IAC valve, go to next step. If no click is heard when applying battery power to IAC valve, replace IAC valve.
   Fig 1: Testing Idle Air Control Valve Connector Terminals

   Courtesy of FORD MOTOR CO.
5. 11) Check Power To IAC Valve
   
   Turn ignition on. Turn A/C and blower motor on. Measure voltage between A/C relay circuit (Gray/Red wire) at IAC valve harness connector and ground. See WIRING DIAGRAMS article. If voltage is greater than 10 volts, go to next step. If voltage is not greater than 10 volts, go to TEST KM .
6. 12) Check IAC Valve Ground
   
   Turn ignition off. Measure resistance of ground circuit (Black wire) between IAC valve harness connector and ground. See WIRING DIAGRAMS article. If resistance is less than 5 ohms, replace IAC valve. If resistance is not less than 5 ohms, repair open in circuit.