You could have 2 problems that might be related.
See if the following helps.
ROUGH, UNSTABLE OR INCORRECT IDLE & STALLING
Engine runs unevenly at idle. If severe enough, vehicle will shake. Idle may vary in RPM. Either problem may cause stalling. Engine idles at incorrect RPM.
Perform preliminary inspection. See PRELIMINARY INSPECTION. Check for Technical Service Bulletins (TSBs).
Check system fuel pressure.
Check the fuel injectors.
Check for contaminated fuel.
Inspect items which can cause an engine to run rich (long term fuel trim significantly in the negative range).
Inspect items that can cause an engine to run lean (long term fuel trim significantly in the positive range).
Inspect for fuel in the fuel pressure regulator vacuum hose.
Check for proper operation of EGR system.
Ensure each injector harness is connected to the correct injector/cylinder.
Inspect for conditions which cause an incorrect idle speed. Check for throttle body tampering, excessive deposits, or damage. Check for restricted air intake system. Check for large vacuum leaks.
Check the Positive Crankcase Ventilation (PCV) valve for proper operation.
Check the Throttle Position (TP) sensor and related circuit wiring.
Check the Exhaust Gas Recirculation (EGR) system for proper operation.
Check the transaxle range switch input with the vehicle in Drive and the gear selector in Drive or Overdrive.
1. Check for proper ignition voltage output using the following steps:
Clip Spark Tester (J 26792) to engine ground.
Connect one end of a spark plug wire to the spark tester. Connect the other end of the spark plug wire to the coil being tested.
Connect another spark plug wire between the remaining tower of the coil being tested and ground.
Crank the engine while observing the spark tester. A crisp Blue spark should be observed.
Repeat procedure for each coil.
2. If spark is not present at the coils, inspect for the following conditions:
Coils - Cracks, carbon tracking/arcing, or a secondary resistance value outside the specified coil resistance range of 5-8 k/ohms.
Spark Plug Wires - Signs of arcing/cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range of 3000 ohms per foot (9840 ohms per meter) or 600 ohms per foot (1968 ohms per meter) for Police models. Spraying the secondary ignition wires with a light mist of water may help locate an intermittent condition. Ignition components will arc to ground when a secondary component is faulty.
Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.
Remove spark plugs and inspect for fouling, cracks, wear, improper gap, burned or damaged electrodes and for improper heat range or reach.
4. If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.
1. Check and inspect engine mechanical condition for the following:
Sticking or leaking valves, worn camshaft lobes, valve timing, bent push rods, worn rocker arms, broken valve springs or excess oil in combustion chambers.
Inspect for incorrect basic engine parts, such as camshaft, cylinder heads, pistons, etc.
1. Check exhaust system for possible restrictions. Inspect for the following:
Inspect exhaust system for damaged or collapsed pipes.
Inspect mufflers for heat distress or possible internal failure.
For possible plugged 3-way catalytic converter.
Inspect for faulty motor mounts.
3. An engine miss condition can be caused by Electromagnetic Interference (EMI) on the reference circuit. EMI can usually be detected by monitoring engine RPM with a scan tool. A sudden increase in RPM with little change in actual engine RPM change, indicates EMI is present. If a condition exists, inspect routing of secondary ignition wires, high voltage components (near ignition control circuits).
4. Inspect for intake and exhaust manifold passages for casting flash.
Attached is a TSB that might be related to the problem.
Images (Click to enlarge)
Saturday, December 25th, 2010 AT 4:11 AM