C Yukon 2WD V8-5.7L VIN R (1999)
Idle Speed: Description and Operation
When there is a problem with the idle refer to Idle Air Control System Diagnosis.
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System too lean (High air/fuel ratio) - Idle speed may be too high or too low. Engine speed may vary up and down, disconnecting the IAC valve
has no effect.
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System too rich (Low air/fuel ratio) - Idle speed too low. Scan counts usually above 80. System obviously rich and may exhibit black exhaust
smoke. Scan tool and/or voltmeter will read a Heated Oxygen Sensor (HO2S) signal fixed above 800 mV (0.8 volt).
