Diagnosis & Repair Procedure
NOTE:
For better performance and results of this diagnostic procedure, usage of appropriate wiring diagram is recommended. See ENGINE PERFORMANCE
in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.
NOTE:
Perform all voltage and resistance tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use an ohmmeter to isolate wiring harness shorts or opens.
- If engine system check has been performed, go to next step. If engine system check has not been performed, perform A-4: ENGINE SYSTEM CHECK under SYSTEM TESTS, then go to next step.
- Turn ignition switch to LOCK position. Perform IAC valve system check. See IDLE AIR CONTROL VALVE SYSTEM CHECK under IDLE CONTROL SYSTEM in SYSTEM & COMPONENT TESTING article. If IAC valve system is faulty, go to next step. If IAC valve system is okay, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO-CODES article. After repair, repeat DTC CONFIRMATION TEST .
- Perform IAC valve component test. See IDLE AIR CONTROL VALVE under IDLE CONTROL SYSTEM in SYSTEM & COMPONENT TESTING article. If IAC valve is faulty, go to next step. If IAC valve is okay, go to step 7 .
- Turn ignition switch to LOCK position. Disconnect ECM 30-pin harness connector C51-2, located under instrument panel, behind glove box. Check ECM and harness connector for poor, loose, corroded or damaged connector terminals. If connector terminals are faulty, repair as necessary and repeat DTC CONFIRMATION TEST . If connector terminals are okay, measure resistance between ECM harness connector C51-2 terminals No. 3 (Light Green/Black wire) and No. 12 (Purple/Black wire). Also measure resistance between ECM harness connector C51-2 terminals No. 10 (Purple/Yellow wire) and No. 11 (Gray/Blue wire). See Figure . If resistances are 70-86 ohms, go to next step. If any resistance is not 70-86 ohms, check for open or short circuit in Light Green/Black wire, Purple/Black wire, Purple/Yellow wire, or Gray/Blue wire between ECM and IAC valve. After repair, repeat DTC CONFIRMATION TEST .
- Check for continuity between ground ECM harness connector C52-2 terminals No. 3 (Light Green/Black wire), No. 10 (Purple/Yellow wire), No. 11 (Gray/Blue wire) and No. 12 (Purple/Black wire). See Figure . If continuity is not found, go to next step. If any continuity is found, repair short to ground in appropriate circuit between ECM and IAC valve. After repair, repeat DTC CONFIRMATION TEST .
- Reconnect ECM and IAC valve harness connectors. Turn ignition switch to ON position. Backprobe and measure voltage between ground and IAC valve 6-pin harness connector C29 and terminals No. 2 (Blue/Black wire) and No. 5 (Blue/Black wire). See Fig 1 . If voltage is 10-14 volts, substitute IAC valve or ECM with a known good unit and repeat DTC CONFIRMATION TEST . If voltage is not 10-14 volts, repair open circuit in Blue/Black wire between AIC valve and main relay. After repair, repeat DTC CONFIRMATION TEST .
- If idle speed as tested in step 2 was higher than specified, check for vacuum leaks from intake manifold, throttle body, PCV valve and EVAP canister purge control system. If problem is found, repair as necessary. After repair, repeat DTC CONFIRMATION TEST . If idle speed as tested in step 2 was not higher than specified, go to next step.
- Check components or parts that could cause low idle, check following:
- Stuck fast idle air valve.
- Air leak between MAF sensor and throttle body.
- Clogged idle air passages.
- Overheated engine.
- High accessory engine load.
- Engine mechanical failure.