Diagnostic Aids

A slow unstable idle may be caused by a system problem that cannot be overcome by the IAC. "Scan" tester counts will be greater than 80 counts if idle is too low and zero counts if it's too high.

• Idle too high  Stop engine. Turn ignition on and ground diagnostic terminal. Wait a few seconds for IAC to seat, then disconnect IAC. Start engine. If idle speed is greater than minimum idle specification, locate and correct vacuum leak. If no leak is detected, adjust minimum idle speed.
• System Too Lean (Air/Fuel Ratio)  Idle speed may be too high or low. Engine speed may vary up and down, and disconnecting IAC does not help. This may set Code 44. The "Scan" tester and/or voltmeter will read an oxygen sensor output less than .3 volt. Check for low regulated fuel pressure or water in fuel. A lean exhaust with an oxygen sensor output fixed greater than .8 volt will be a contaminated sensor. This may set Code 45 or 61.
• System Too Rich (Low Air/Fuel Ratio)  Idle speed too low. The "Scan" tester counts usually greater than 80. System is rich and may exhibit Black exhaust smoke. The "Scan" tester and/or voltmeter will read an oxygen sensor signal fixed greater than .8 volt. Check for fuel in pressure regulator hose, high fuel pressure or injector leaking or sticking.
• MAF Sensor  If idle is rough or unstable, disconnect MAF sensor. If idle improves, substitute a known good sensor. MAF sensor may be tested for being out of calibration using MAF Tester (J 36101).
• Throttle Body  Remove IAC and inspect bore for foreign material or evidence of IAC valve dragging the bore.
• A/C Compressor or Relay Failure  If the A/C control relay drive circuit is shorted to ground or if the relay is faulty, an idle problem may exist.