Possible Causes & Corrections

Check the following items:

• Search for bulletins.
• Verify that PCM grounds are clean, tight and in the proper locations.
• If there are no engine mechanical faults, fill fuel tank with a known high quality fuel that meets the vehicle's minimum octane requirements. Road test vehicle and re-evaluate the vehicle performance.
• 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 for conditions that may cause engine to run lean: Water intrusion in HO2S connector, exhaust leak between HO2S and engine, any vacuum leaks, incorrect fuel pressure, restricted fuel injectors, or fuel contamination. Check for any vacuum hoses that are split, kinked or improperly connected.
• Check spark plugs for the proper heat range and gap.
• Low engine coolant.
• Restricted air flow to radiator or restricted coolant flow through the radiator.
• Inoperative cooling fan.
• The correct coolant solution should be a 50/50 mix of DEX-COOL(tm) or equivalent antifreeze coolant and water.
• Check for excessive oil in combustion chamber (leaking valve seals).
• Check for low cylinder compression.
• Check combustion chambers for excessive carbon buildup. Clean combustion chamber by using top engine cleaner.
• Inspect for incorrect basic engine parts. Inspect camshaft, cylinder heads, pistons, etc.
• Inspect the Park/Neutral Position (PNP) switch operation.
• Inspect transmission Torque Converter Clutch (TCC) operation. The TCC applying too soon can cause engine to spark knock. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.