Possible Causes & Corrections

Check the following items:

• Search for bulletins.
• Verify that PCM grounds are clean, tight, and in the proper locations.
• Check the owner's driving habits. Is the A/C on or defroster mode on full time? Are tires at the correct pressure? Are tires the correct size? Are there excessively heavy loads being carried? Is acceleration rate too much, too often? Remove air filter element and inspect for dirt or for restrictions.
• Inspect the type, quality and alcohol content of the fuel. Oxygenated fuels have lower energy and may deliver reduced fuel economy.
• Inspect fuel injectors. See FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 2.2L SONOMA & S10 PICKUP article.
• Inspect for incorrect fuel pressure. See FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 2.2L SONOMA & S10 PICKUP article.
• Inspect for a restricted fuel filter.
• Inspect for a contaminated fuel condition.
• Inspect that each fuel injector harness is connected to the correct injector and cylinder. Relocate injector harnesses as necessary.
• Inspect for foreign material accumulation in the throttle bore, coking on the throttle valve, or on throttle shaft.
• Inspect for the following that may cause the engine to run rich: Water intrusion in the HO2S connector, engine oil contaminated by fuel, EVAP canister purge condition, incorrect fuel pressure, leaking fuel pressure regulator, leaking fuel injectors, any vacuum hoses that are split, kinked, or improperly connected. Check for an air intake duct that is collapsed or restricted or an air filter that is dirty or restricted.
• Inspect air intake system and crankcase for air leaks.
• Inspect the crankcase ventilation valve for proper operation. Place a finger over the inlet hole in the valve end several times. The valve should snap back. If not, replace PCV.
• Inspect for an inaccurate speedometer.
• Use a scan tool in order to monitor the Knock Sensor (KS) system for excessive spark retard activity.
• Inspect for proper ignition voltage output with Spark Tester (J-26792).
• Remove spark plugs and inspect for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits.
• An improper spark plug gap will cause a driveability problem.
• Determine the cause of the fouling before replacing spark plugs.
• Visually and physically inspect the secondary ignition for ignition wires arcing to ground or ignition wires for proper routing.
• Soaking the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water. Inspect for loose ignition coil grounds.
• Inspect for low engine coolant level.
• Inspect engine thermostat for proper operation and for the correct heat range.
• Inspect engine low compression. Low compression can be caused by a sticking or leaking valves, worn camshaft lobes, valve timing, bent push rods, worn rocker arms or broken valve springs. Check for excessive oil in combustion chamber, caused by leaking valve seals.
• For incorrect basic engine parts inspect, such as camshaft, cylinder heads or pistons, etc.
• Visually and physically check the vacuum hoses for splits, kinks, and proper connections and routing as shown on Vehicle Emission Control Information label.
• Inspect the transmission Torque Converter Clutch (TCC) operation. The scan tool should indicate a RPM drop, when the system commands the TCC on.
• Inspect exhaust system for a possible restriction. Inspect for exhaust system for damaged or collapsed pipes, inspect mufflers for heat distress or possible internal failure. Inspect for plugged three-way catalytic converters by comparing the exhaust system back pressure on each side of the engine. Inspect the back pressure by removing the Secondary Air Injection (AIR) check valves near exhaust manifolds.
• Electromagnetic Interference (EMI) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM with little change in actual engine RPM change indicates EMI is present. Inspect for high voltage components, near ignition control circuits, if a condition exists.
• Inspect the Park/Neutral Position (PNP) switch circuit.
• Inspect intake and exhaust manifold passages for casting flash.
• Inspect brake system for dragging or improper operation. Verify that vehicle operator does not drive with a foot on the brake pedal.