For 1990-2009 cars

Cause | Correction
--- | ---
Abnormalities consist of severe cracking, bumps, or missing areas in the accessory drive belt Abnormalities in the accessory drive system and/or components may cause engine RPM variations and lead to a misfire DTC. A misfire code may be present without an actual misfire condition. | Replace the drive belt. Refer to Drive Belt Tensioner Replacement .
Worn, damaged, or mis-aligned accessory drive components or excessive pulley runout may lead to a misfire DTC. A misfire code may be present without an actual misfire condition. | Inspect the components, and repair or replace as required.
Loose or improperly installed engine flywheel or crankshaft balancer A misfire code may be present without an actual misfire condition. | Repair or replace the flywheel and/or balancer as required. Refer to Engine Flywheel Replacement or Crankshaft Balancer Replacement .
Restricted exhaust system A severe restriction in the exhaust flow can cause significant loss of engine performance and may set a DTC. Possible causes of restrictions include collapsed or dented pipes or plugged mufflers and/or catalytic converters. | Repair or replace as required.
Improperly installed or damaged vacuum hoses | Repair or replace as required.
Improper sealing between the intake manifold and cylinder heads or throttle body. | Replace the intake manifold, gaskets, cylinder heads, and/or throttle body as required.
Worn or loose rocker arms The rocker arm bearing end caps and/or needle bearings should be intact and in the proper position. | Replace the valve rocker arms as required.
Worn or bent pushrods | Replace the pushrods.
Stuck valves Carbon buildup on the valve stem can cause the valve not to close properly. | Repair or replace as required.
Excessively worn or mis-aligned timing chain | Replace the timing chain and sprockets as required.
Worn camshaft lobes | Replace the camshaft and valve lifters.
Excessive oil pressure A lubrication system with excessive oil pressure may lead to excessive valve lifter pump-up and loss of compression. |

• | Perform an oil pressure test. Refer to Oil Pressure Diagnosis and Testing .

• | Repair or replace the oil pump as required.

Faulty cylinder head gaskets and/or cracking or other damage to the cylinder heads and engine block cooling system passages. Refer to Diagnostic Starting Point - Engine Cooling . Coolant consumption may or may not cause the engine to overheat. |

• | Inspect for spark plugs saturated by coolant. Refer to Spark Plug Inspection .

• | Inspect the cylinder heads, engine block, and/or head gaskets.

• | Repair or replace as required.

Worn Piston Rings Oil consumption may or may not cause the engine to misfire. |

• | Inspect the spark plugs for oil deposits. Refer to Spark Plug Inspection .

• | Inspect the cylinders for a loss of compression. Refer to Engine Compression Test .

• | Perform cylinder leak down and compression testing to identify the cause.

• | Repair or replace as required.