Patent ID: 8122869

Claim:
An air-fuel ratio control system of a multi-cylinder internal combustion engine provided with, as an intake air amount control means, a throttle valve and an opening characteristic control means for controlling at least one of a working angle and a valve lift of at least one of an intake valve and an exhaust valve, wherein said system controls a fuel injection amount based on an output of at least one of a sensor detecting an air-fuel ratio of exhaust gas flowing through an exhaust passage and a sensor detecting an oxygen concentration of exhaust gas flowing through the exhaust passage so as to perform air-fuel ratio feedback control, wherein said air-fuel ratio feedback control includes learning control which is performed by correcting a relationship of the output of said sensor and a feedback value based on a feedback learning correction value which is learned and determined based on the output of said sensor during said air-fuel ratio feedback control and, when the intake air amount is controlled by only said throttle valve when newly learning and determining said feedback learning correction value, while at least one of said working angle and said valve lift is made a constant value of at least a predetermined value.