Variable Valve Timing
Most late-model vehicles have VVT variable valve timing that delivers smooth idle and low-speed operation while providing performance and horsepower at higher RPM's. Manufacturers install camshafts with fixed lift and duration in engines without VVT. A small passenger car would have camshaft lobs with less duration and lift than a high-performance sports car would. With variable valve timing, they get the best of both worlds.
There are different ways to accomplish variable timing. Phasers and special sprockets smoothly advance the timing as engine speeds increase and valve systems that increase the duration and lift at certain RPMs with separate cam lobes. Some models used a hydraulically controlled pin activating a rocker arm and cam lobe with more lift and duration. This greatly increased high-speed performance, and we were amazed. It suddenly transformed an average engine into a high-performance machine.
Symptoms of faulty VVT systems include a rough idle and poor high-speed engine performance. The solenoids and actuators used to 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 that forms from unchanged oil. A tarnished actuator may not release or engage.
The actuators and solenoids on most systems are ground controlled by a driver in the engine control module. Often, if there is no change in engine operation when the proper wire of the solenoid is grounded, there's something wrong with the variable valve timing actuator itself. Always check with the manufacturer of the engine for TSB's, tips on diagnosis, and any special procedures.