VVT, or Variable Valve Timing, is a newer system, about a few years old now, that replaces EGR to recirculate unburnt gasses back into the combustion chamber and reduce emissions. VVT uses engine oil pressure to change the way the motor runs to do this. At running speeds, the engine oil will be sent into the camshaft phasers which change the timing. When you are travelling at speed, the phasers will advance the camshafts so that the exhaust valves and intake valves are open at the same time for a very short duration, drawing air and those nasty gasses back into the combustion chamber so that it can be ignited and less of it makes its way into the outside air. When the vehicle slows down, the phasers then retard the timing back to normal operation.
There are a few things that can affect driveability in VVT-equipped motor vehicles. If you use a thicker engine oil than the manufacturer specifies then it can slow the action of the phasers, causing racing of the engine as you slow down because the cams will not retard properly. There are little mesh screens, sometimes on the phasers, sometimes on the controlling solenoid. If you are using old and dirty oil, these screens can become obstructed, not allowing the flow of oil and causing poor engine performance. Also, low oil capacity can have an ill effect on the VVT system. This can cause damage to your engine and become costly to repair.
It is crucial that you keep your oil changed, use the proper viscosity and maintain your engine’s oil level. Doing this will help you avoid unnecessary headaches and keep you on the road.