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.
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 balancer A misfire code may be present without an actual misfire condition. | Repair or replace the flywheel and/or balancer as required.
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 head or throttle body. | Replace the intake manifold, gaskets, cylinder head, and/or throttle body as required.
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.
Damage to the MAP sensor housing and/or O-ring seal | Replace the intake manifold.
Worn or loose valve 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 valve lash adjusters | Replace the valve lash adjusters.
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 rocker arms.
Excessive oil pressure |

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

• | Repair or replace the oil pump as required.

Faulty cylinder head gasket and/or cracking or other damage to the cylinder head and engine block cooling system passages. Coolant consumption may or may not cause the engine to overheat. |

• | Inspect for spark plugs saturated by coolant.

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

• | 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.

• | 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 electronic communications (DIS or coil per cylinder) and severe reluctor ring damage may exhibit periodic loss of crankshaft position, stop delivering a signal, and then re-sync the crankshaft position.

• | 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.

• | Systems with mechanical communications (high voltage switch) and severe reluctor ring damage may cause additional pulses and effect fuel and spark delivery to the point of generating a P0300 DTC or P0336.

Replace the sensor and/or crankshaft as required.