To detect the sound-vibration state of an engine intake system to perform fail-safe control at the occurrence of abnormality.

When the sound-vibration level of an engine intake system is abnormal or an afterburning phenomenon or a backfire occurs, each abnormality is suppressed by the operation of the valve timing and the like of an electrically controlled throttle valve and solenoid driven intake and exhaust valves. Noise and vibration inside and outside of a cabin are thereby reduced, and the durability of parts around the intake system is improved.