For 1990-2009 cars

Cause | Correction
--- | ---
Abnormalities, extreme 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 Replacement.
Worn, damaged, or mis-aligned accessory drive components or pulley runout above acceptable tolerances may lead to a misfire DTC. A misfire code may be present without an actual misfire condition. | Inspect the components: Repair or replace as required.
Loose or incorrectly 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 Replacementt or Crankshaft Balancer Replacement.
Restricted exhaust system. An extreme 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. Refer to engine exhaust for the required procedure.
Incorrectly installed or damaged vacuum hoses. | Repair or replace as required.
Incorrect sealing between the intake manifold and cylinder heads, intake manifold and throttle body and/or pressure relief valve and intake manifold. | Replace the intake manifold, plenum duct, cylinder heads, throttle body, pressure relief valve or gaskets as required.
Incorrectly installed or damaged EVAP purge solenoid and/or O-ring seal. | Repair or replace the EVAP purge solenoid as required.
Worn or loose Stationary Hydraulic Lash Adjusters (SHLAs), valve rocker arms. The stationary hydraulic lash adjusters (SHLAs), valve rocker arm, roller bearing should be intact and in the correct position | Replace the SHLAs, valve rocker arms, as required.
Sticking valves. Carbon buildup on the valve stem can cause the valve not to close correctly. | Repair or replace as required.
Timing chain or chains worn or mis-aligned above acceptable tolerances. | Replace the timing chain or chains and sprockets as required.
Worn camshaft lobes. | Replace the camshaft or camshafts and high Stationary Hydraulic Lash Adjusters (SHLAs), valve lifters.
Oil pressure above acceptable tolerances. A lubrication system with oil pressure above acceptable tolerances may lead to valve lifter pump-up above acceptable tolerances 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 cylinder 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, cylinder 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.

A damaged crankshaft reluctor wheel. A damaged crankshaft reluctor wheel can result in different symptoms depending on the severity and location of the damage.

• | Systems with EXTREME reluctor ring damage may exhibit periodic loss of crankshaft position, stop delivering a signal, and then re-sync the crankshaft position.

• | Systems with SLIGHT reluctor ring damage may exhibit no loss of crankshaft position and no misfire may occur. However, a P0300 DTC may be set.

Replace the crankshaft as required.