A variable air induction control system for an internal combustion engine. The engine intake passage is divided into a long and small diameter main passage and a short and large diameter auxiliary passage. The auxiliary passage is provided with a valve which is opened and closed to adjust the air flow rate. The system is arranged such that, in accordance with the cylinder pressure, the intake air passes through the main intake passage during low speed engine operation and through both the main and auxiliary passages during high speed engine operation, whereby the air induction efficiency (charging efficiency) is enhanced and the engine output increased. As knocking is more likely to occur when the air induction efficiency is high, the opening/closing of the valve is controlled depending on whether or not knocking occurs. Moreover, it may be arranged such that when knocking does occur, it is first coped with by retarding the ignition and if knocking cannot be eliminated in this way, the air intake is adjusted.