Engine runs unevenly at idle. If bad enough, vehicle will shake. Idle RPM may vary. Engine idles at incorrect RPM.
Check the following items:
Check TP sensor for sticking and binding. Check for correct TP sensor voltage. See FUEL SYSTEMS in appropriate SERVICE & ADJUSTMENT SPECIFICATIONS article.
Check to see if condition is caused by engine running either rich or lean.
Check Park Neutral Position (PNP) switch circuit. Ensure PNP switch is properly adjusted.
Check for poor quality or alcohol contaminated fuel.
Check in-line fuel filter. Replace if dirty or clogged.
Check intake and exhaust manifold passages for casting flash.
Check fuel system for incorrect fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
Check fuel injectors. Perform injector balance test. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
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 for fuel in pressure regulator vacuum hose. If fuel is present, replace regulator.
Check injector harness locations. Ensure injectors are connected to correct injector/cylinder according to firing order.
If rough idle occurs only when engine is hot, check PCV valve for proper operation. Check evaporative emission control system.
Check PCV system for proper operation.
Check engine compression. Check for incorrect valve timing, bent push rods, broken valve springs or worn camshaft lobes.
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.
Ensure initial ignition timing is properly set.
Check Knock Sensor (KS) system for excessive retard.
Check engine idle speed (both base and PCM idle).
Check Idle Air Control (IAC) system. Check for foreign material in IAC bore.
Check EGR system for proper operation.
Check Power Steering Pressure (PSP) switch circuit.
Monday, March 15th, 2010 AT 6:55 AM