Intake air amount control system and method for internal combustion engine

A method of controlling an amount of intake air supplied to an internal combustion engine that is installed on a vehicle, and includes a variable valve-operating mechanism which is capable of continuously changing a lift of an intake valve, an intake air amount-adjusting valve which is disposed in an intake passage and is capable of adjusting an intake air amount by changing an opening thereof, an actuator that drives the variable valve-operating mechanism, and an auto cruise function for performing an auto cruise operation in which a vehicle speed of the vehicle is held at a target vehicle speed, comprising:

• an auto cruise-determining step of determining whether or not the engine is in the auto cruise operation;
• a target lift-holding step of holding a target lift which is a target of the lift of the intake valve, at a predetermined lift, when it is determined that the engine is in the auto cruise operation;
• and
• an intake air amount-adjusting valve control step of controlling the intake air amount by changing the opening of the intake air amount-adjusting valve when the target lift is held at the predetermined lift in said target lift-holding step.