Engine oil level overfull, causing aeration

Drain excess oil and adjust oil level to proper specification.

Worn or loose rocker arms--The rocker arm bearing end caps and/or needle bearings should intact within the rocker arm assembly.

Replace the valve rocker arms as required.

Worn or bent pushrods

Replace the pushrods.

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 valve lifters.

Sticking lifters

Replace as required.

Malfunctioning camshaft position actuator--Improper viscosity oil, contaminated oil, or a plugged or missing camshaft position actuator filter can cause the camshaft position actuator locking pin to malfunction.