Diagnostic Aids
A slow, unstable or fast idle may be caused by a non-IAC system problem that cannot be overcome by IAC valve. Out of control range IAC counts will be above 60 as observed on scan tool if idle is too low, and zero counts if idle is too high. Following checks should be made to repair a non-IAC system problem:
- Vacuum leak (high idle) - If idle is too high, stop engine. Using IAC Motor Analyzer (J39027-A), fully extend IAC. Start engine. If idle speed is 800 RPM or more, locate and correct vacuum leak, including PCV system. Check for binding of throttle blade or linkage.
- Lean heated oxygen sensor signal (high air/fuel ratio) - Idle speed may be too high or too low. Engine speed may vary up and down, and disconnecting IAC valve does not help. If DTC P0131, P0151, P0171, or P0174 is stored in memory, perform appropriate test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - RODEO & RODEO SPORT 2.2L article. On scan tool HO2S No. 2 voltage will be less than 100 mV. Check for low regulated fuel pressure, water in fuel, or a restricted injector.
- Rich heated oxygen sensor signal (low air/fuel ratio) - Idle speed will be too low. On scan tool IAC counts will usually be 80 or more. System is obviously rich and may exhibit black smoke in exhaust. H02S voltage will be fixed at about 750 mV. Check for high fuel pressure, or a leaking or sticking injector. A silicon-contaminated heated oxygen sensor will show an HO2S voltage slow to respond on scan tool.
- Throttle body - Remove IAC valve and inspect throttle bore for foreign material.
- IAC valve electrical connections - IAC valve terminal connections should be carefully checked for proper contact.