For 1990-2009 cars

Cause | Correction
--- | ---
Abnormalities, such as 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 - Accessory .
Worn, damaged, or mis-aligned accessory drive components or above acceptable 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 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 Replacement 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. | Inspect the exhaust system for restrictions. Refer to Restricted Exhaust .
Incorrectly installed or damaged vacuum hoses. | Inspect the vacuum hose routing, Refer to Evaporative Emissions Hose Routing Diagram .
Incorrect 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 .
Incorrectly 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 Manifold Absolute Pressure Sensor Replacement
Worn or loose rocker arms. The rocker arm bearing end caps and/or needle bearings should be intact and the rocker arm in the correct position. | Replace the valve rocker arms, as required. Refer to Valve Rocker Arm and Push Rod Replacement .
Worn or bent pushrods. | Replace the valve rocker arms, as required. Refer to Valve Rocker Arm and Push Rod Replacement .
Stuck valves. Carbon buildup on the valve stem can cause the valve not to close correctly. | Repair or replace, as required. Refer to Cylinder Head Disassemble .
A worn or mis-aligned timing chain above acceptable tolerances. | Replace the timing chain and sprockets, as required. Refer to Camshaft Timing Chain and Sprocket Replacement .
Worn camshaft lobes. | Replace the camshaft and valve lifters. Refer to Camshaft Replacement .
Oil pressure above acceptable tolerances. A lubrication system with oil pressure above acceptable tolerances may lead to above acceptable valve lifter pump-up and loss of compression. |

1. Perform an oil pressure test. Refer to Oil Pressure Diagnosis and Testing .
2. Repair or replace the oil pump, as required. Refer to Oil Pump, Screen, and Crankshaft Oil Deflector Replacement .

Failed cylinder head gaskets and/or cracking or other damage to the cylinder heads and engine block cooling system passages. 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. Refer to Coolant in Combustion Chamber .

• | Refer to Cylinder Head Replacement - Left Side .

| or

| Refer to Cylinder Head Replacement - Right Side .

• | 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 a cylinder leak down test. Refer to Cylinder Leakage 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.

• | Severe reluctor ring damage may exhibit periodic loss of crankshaft position, stop delivering a signal, and then sync the crankshaft position.

• | 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 sensor and/or crankshaft, as required. Refer to Crankshaft and Bearing Removal .

or

Crankshaft Position Sensor Replacement .