Possible Cause & Correction

Check the following items:

• Check for incorrect valve timing, bent push rods, broken valve springs or worn camshaft lobes.
• Check for sticking or leaking valves.
• Check EGR valve for leaking base gasket or valve hanging open.
• Check for engine vacuum leaks and/or engine not tuned to specifications.
• Check ignition module ground and power feed circuits for poor or loose connections.
• Check air induction system for restrictions or air leaks. Also check for air leaks between Mass Airflow (MAF) sensor and throttle body. Check MAF sensor for proper operation.
• Check fuel injectors. Perform injector balance test. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
• Check fuel system. Perform BASIC FUEL SYSTEM CHECKS. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
• Using Spark Tester (J-26792), check available output voltage of ignition coil.
• Check for crossfire between spark plugs and spark plug wires.
• Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits. Also, check condition of spark plug wires. Spray spark plug wires with a fine mist of water to check for shorts.
• Check for proper Crankshaft Position (CKP) and Camshaft Position (CMP) sensor resistance.
• Check ignition system for faulty ground and power feed circuits.
• Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter.
• Check intake and exhaust manifold passages for casting flash.
• Check harmonic balancer interrupter rings for missing, broken or bent vanes.
• Check for a low engine coolant level.
• Check the engine thermostat for the correct operation and heat range.
• Test the Torque Converter Clutch (TCC).
• Check the charging system. A bad diode in the alternator can allow A/C noise to enter the electrical system. This may affect the engine controls system operation.
• Check the transaxle range switch circuit and be sure the scan tool indicates the vehicle is in drive with the gear selector in Drive or in Overdrive.