To enable valve closing failure of an intake air flow control valve such as a swirl control valve to be accurately detected by a simple configuration.
A specified area on the high load-high rotation side in a valve opening area of a swirl control valve(SCV), for example, an area where the coefficient of fluctuation of intake air flow (qa) when the throttle valve opening is changed by 10%, is within 3%, and the difference between the intake air flows at the times of SCV opening and closing is 5 g/s or more, is regarded as a valve closing failure diagnostic area. The intake air flow to an engine is detected in this area, and when the intake air flow is smaller than a threshold value, the swirl control valve is judged to be failed to close the valve. In this case, when the ISC valve fails to open it, the failure judgment of the swirl control valve is prohibited. Further, when the water temperature of the engine is, for example, 80 degrees C or less, the failure judgment of the throttle control valve is prohibited.
MAYAHARA KENJI
SAKATA YUJI
