Possible Causes & Corrections

Check for the following items:

• 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 open in ignition system ground circuit. Ensure initial ignition timing is correct.
• Check fuel system for incorrect fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
• Check for plugged injectors. Perform injector balance test. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
• Check for poor fuel quality or water-contaminated fuel.
• Ensure TP sensor does not stick or bind. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT).
• Check Manifold Absolute Pressure (MAP) sensor response and accuracy. See appropriate SYSTEM & COMPONENT TESTING article.
• Check canister purge system for proper operation.
• Check EGR valve for proper operation.
• Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in appropriate BASIC DIAGNOSTIC PROCEDURES article.
• Check Heated Oxygen Sensor (HO2S) for contamination. This will cause a false high voltage signal to PCM. PCM will respond by leaning out air/fuel ratio.
• Ensure correct PROM is installed in PCM. Check dealer for latest application.
• Check charging system output. Repair if output is less than 9 volts or greater than 16 volts.