For 1990-2009 cars

Cause | Correction
--- | ---
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.
Stuck valves Carbon buildup on the valve stem can cause the valve to not close properly. | Repair or replace as required.
Excessively worn or mis-aligned timing belt | Replace the timing belt and sprockets as required.
Worn camshaft lobes | Replace the camshaft and valve lash adjusters.
Sticking valve | Replace as required.
Worn or damaged pushrods | Inspect the pushrods for excessive wear, bent condition or broken tip. Replace as required.
Broken valve springs | Inspect valve springs and replace as required.
Excessive valve lash | Inspect the valve lash adjusters and replace as required.