When the engine power output is below normal, check for the following, as necessary:
Overheating of the cooling system.
Leaks in the vacuum system.
Leaking of the fuel pump or hoses.
Unadjusted valve timing.
A blown head gasket.
A slipping clutch disc or unadjusted pedal.
Excessive piston-to-bore clearance.
Worn piston rings.
A worn camshaft.
Sticking valve(s) or weak valve spring(s).
A poorly operating diverter valve.
A faulty pressure regulator valve (Auto. Trans.).
Low fluid level (Auto. Trans.).
Fault with the computerized engine control system.