Valve timing control system for internal combustion engine

A valve timing control system for an internal combustion engine, for controlling valve timing for opening and closing at least one of an intake valve and an exhaust valve by changing a cam phase which is a phase of at least one of an intake cam and an exhaust cam, relative to the crankshaft, the engine having a camshaft on which at least one of the intake cam and the exhaust cam is arranged,

• the valve timing control system comprising:
• a cam phase-varying device for varying the cam phase by rotating the camshaft relative to the crankshaft;
• deceleration fuel cut-off operation-determining means for determining whether or not the engine is performing a fuel cut-off operation in which supply of fuel to the engine is stopped during deceleration;
• and
• cleaning control means for forcibly driving said cam phase-varying device within a predetermined cam phase range when a predetermined delay time has elapsed after the deceleration fuel cut-off operation is started, to thereby prevent undesired locking of said cam phase-varying device.