C 2500 Truck 2WD V8-5.7L VIN R (1997)
Idle Speed: Testing and Inspection
Idle Speed
When there is a problem with idle air control system or refer to VCM Outputs Diagnosis. Refer to Diagnostic Tables.
System too lean (High air/fuel ratio) - Idle speed may be too high or too low. Engine speed may vary up and down, disconnecting IAC does not help.
May set DTC P0171. Refer to DTC P0171 Fuel Trim System Lean Bank 1. Refer to Diagnostic Trouble Code Tables.
Scan tool and/or voltmeter will indicate a heated oxygen sensor output less than 300 mV (0.3V). Check for low regulated fuel pressure or water in fuel.
A lean exhaust with a Heated Oxygen Sensor (HO2S) output fixed above 800 mV (0.8V) may be the result of a contaminated sensor, usually silicone.
This may also set a DTC P0172. Refer to DTC P0172 Fuel Trim System Rich Bank 1. Refer to Diagnostic Trouble Code Tables.
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 (0.8V). Refer to Diagnostic Trouble Code Tables.
