For 1990-2009 cars

Cause | Correction
--- | ---
Abnormalities (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 Replacement .
Worn, damaged, or mis-aligned accessory drive components or excessive pulley runout and 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 pulley (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 Pulley 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. Refer to Intake Manifold Replacement , Cylinder Head Replacement or Throttle Body Assembly Replacement .
Improperly installed or damaged MAP sensor (The sealing grommet of the MAP sensor should not be torn or damaged.) | Repair or replace the MAP sensor as required. Refer to Mass Airflow Sensor Replacement .
Damage to the MAP sensor housing and/or O-ring seal | Repair or replace as required. Refer to Manifold Absolute Pressure Sensor Replacement .
Worn or faulty rocker arm (The rocker arms may be loose on the rocker arm shaft. The rocker arm adjusting screw tips or the cam riding surface may be worn) | Replace the valves. Refer to Cylinder Head Disassemble .
Stuck valves (Carbon buildup on the valve stem can cause the valve not to close properly.) | Repair or replace as required. Refer to Cylinder Head Disassemble .
Excessively worn or mis-aligned timing belt | Replace the timing belt and sprockets as required. Refer to Timing Belt Replacement .
Worn camshaft lobes | Replace the camshaft. Refer to Camshaft Replacement .
Faulty cylinder head gaskets and/or cracking or other damage to the cylinder heads and engine block cooling system passages. Refer to A Diagnostic Starting Point - Engine Cooling. 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 Visual Inspection in Engine Controls. 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 Visual Inspection in Engine Controls. Refer to Spark Plug Inspection

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

• | Perform cylinder leak down test.

• | 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 electronic communication (DIS or coil per cylinder) and slight reluctor ring damage may exhibit no loss of crankshaft position and no misfire may occur. However, a P0300 DTC may be set. | Repair or replace as required.