Worn or loose rocker arms.

The rocker arm bearing end caps and/or needle bearings should be intact within the rocker arm assembly.

Replace the valve rocker arms, as required. Refer to Valve Rocker Arm and Push Rod Replacement.

Worn or bent pushrods.

Replace the pushrods, 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.

Sticking lifters.

Replace the camshaft and valve lifters. Refer to Camshaft Replacement.

Cut or damaged oil pump screen O-ring seal which may cause aeration of the engine oil.

Repair, as required. Refer to Cylinder Deactivation (Active Fuel Management) Oil Pressure Relief Valve Diagnosis and Testing.

Incorrect operation of the active fuel management oil pressure relief valve.

Repair, as required. Refer to Cylinder Deactivation (Active Fuel Management) Oil Pressure Relief Valve Diagnosis and Testing.

Incorrect operation of the active fuel management system

Repair, as required. Refer to Cylinder Deactivation (Active Fuel Management) Oil Pressure Relief Valve Diagnosis and Testing.