Variable valve timing, or VVT, has been in existence since the 1960s. This is basically the name given to a very wide array of techniques that is used to generate greater power from the engine at higher speeds or when the engine is under a load pressure.
Different car manufacturers have different variable valve timing systems, yet almost all of them depend on a variable valve timing solenoid to control the flow of oil to the VVT system when engaged because VVT does not work on idle, and only comes into play during higher speeds/ when there is load needs. Thus when the solenoid is activated, oil is sent from the system to lubricate the VVT chain and gear
http://www.automobileglobe.com/how-to-know-a-failed-vvt-solenoid/