Possible Cause & Correction

Check the following items:

• Visually check vacuum hoses for splits, kinks and proper connections as shown on vehicle emission control information label.
• Check ignition wires for cracking, hardness and proper connections at spark plugs. Spray spark plug wires with a fine mist of water to check for shorts.
• Check wires for pinches, cuts and proper connections.
• Check fuel pressure. See FUEL SYSTEM PRESSURE TEST under BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
• Check for poor quality or alcohol/water contaminated fuel.
• Check for fouled spark plugs.
• Ensure the installed PROM and/or PCM is correct for that particular vehicle. Check with dealer for latest application information.
• Check for a binding or sticking TP sensor. Voltage should increase steadily as throttle is moved toward Wide Open Throttle (WOT). Also check related wiring.
• Ensure PCM-controlled idle speed is correct.
• Check EGR operation.
• Check engine cooling system thermostat for proper operation and heat range.
• Check ignition control system ground and power feed circuits.
• Check canister purge system for proper operation.
• Check charging system output. Repair charging system if voltage is less than 9 volts or more than 16 volts.
• Check fuel injectors. Perform injector balance test. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
• Check injector harness locations. Ensure injectors are connected to correct injector/cylinder according to firing order.
• Check for proper Crankshaft Position (CKP) and Camshaft Position (CMP) sensor resistance. Check for intermittent ignition feed or ground circuits.
• Check Heated Oxygen Sensor (HO2S) ground (corroded threads in exhaust manifold or pipe).
• Check for air leaks between Mass Airflow (MAF) sensor and throttle body.
• Check air induction system for damage, restriction or air leaks.
• Check for intake valve deposits.
• Check Manifold Absolute Pressure (MAP) and MAF sensor values and related wiring.
• Check for excessive exhaust system backpressure.