Variable Valve Timing

A cutaway view of a variable valve timing system.

Most late-model vehicles have some form of (VVT) variable valve timing. Variable valve timing delivers smooth idle and low-speed operation and performance and horsepower at higher RPMs.

Variable valve timing actuator explained.

There are different ways to accomplish this. Some systems change the timing by opening the intake valve sooner, allowing more air-fuel mixture to enter the combustion chamber.


Alternating between two camshaft lobes for each cylinder provides a smooth idle, low-speed, and high-speed performance.

EGR valve.

Holding the exhaust valve open a little longer allows a small amount of exhaust to enter the chamber, reducing NOx formation. As a result, manufacturers have designed engines without EGR valves.

A cutaway view of a variable valve timing system.

Test the solenoid and its circuit for resistance with an ohmmeter. A faulty VVT solenoid or valve could produce a rough idle or poor high-speed engine performance. The solenoids and actuators that control these systems can become clogged or have electrical issues. Unchanged oil is a big problem. The solenoids, control valves, and passages become clogged with a gel from neglected and unchanged oil. A tarnished actuator may not release or engage.