Abstract: To inhibit an air pulsating sound resulting from the opening and closing of the air control valve in a cold engine and to improve controllability of ISC functions in an assist air supply apparatus. When an engine is cold based on a cooling water temperature sensor, opening control is performed so as to control the amount of supplied assist air by controlling the opening degree of an air control valve. When the engine is warming-up, injection synchronization control is performed, in which opening and closing of the air control valve are controlled in synchronization with fuel injection from the fuel injection valves. Therefore, it is possible to suppress air pulsating noise resulting from the opening and closing the air control valve when the engine is warming up and to improve controllability of ISC functions in an assist air supply apparatus.

Abstract: The invention provides a malfunctional detecting apparatus for an assist air control system for internal combustion engines, which is capable of detecting malfunction such as the deterioration of the response of air control valve. A fuel injection valve is provided at downstream side of a throttle valve in an intake passage, and assist air passage is introduced into an injection port of the fuel injection valve. The assist air passage is open or closed by an air control valve which is operated in synchronism with the fuel injection valve. The assist air passage pressure sensor for detecting assist air pressure is provided in the assist air passage. The malfunction of the air control valve is judged based on the assist air pressure immediately after the air control valve is operated.