With extended time and use, the clearances between the lobes or rocker arms and the valve stems they act on can become greater. That often leads to a clattering noise or more engine vibration that ...

The standard VVT approach is to use electronic controls to adjust the mechanical actuation between the engine's cam lobes and the valve stems ... burning of the fuel-air charge.

Idle problems can often, but not always, stem ... the idle air control valve. It is a valve or a device that opens and closes to release air or fluid flow (air in this case) into the engine.