A method of controlling an internal combustion engine employs a microcomputer to control the fuel supply to the engine as well as the ignition timing thereof on the basis of measurement of the air quantity fed to the engine. For measuring the air quantity charged to the engine with high accuracy, the intake air flow fed to the engine is sampled in synchronism with the pulsating variation thereof. A value obtained by averaging the sampled values is used as the intake air quantity on the basis of which the fuel supply and the ignition timing are arithmetically determined.