Abnormality detection apparatus for intake system of internal combustion engine

The present invention relates to an abnormality detecting apparatus for an intake system of an internal combustion engine, and more particularly to an apparatus for detecting an abnormality of the intake system of the internal combustion engine which has a bypass passage bypassing a throttle valve and an idling control valve for controlling the amount of air supplied through the bypass passage. An abnormality detecting apparatus for an intake system of an internal combustion engine, which detects an abnormality of the intake system, is disclosed. The intake system has a throttle valve, a bypass passage bypassing the throttle valve, and an idling control valve for controlling the amount of air supplied through the bypass passage to the engine. A total intake air amount supplied to the engine is calculated. An amount of intake air supplied through the bypass passage is calculated based on a valve opening control quantity for the idling control valve. A parameter indicative of a leak air amount of the intake system is calculated according to the result of a comparison between the calculated total intake air amount and the amount of intake air supplied through the bypass passage. It is determined that the intake system is abnormal when the parameter indicative of the leak air amount is greater than a determination threshold in an engine operating condition where the throttle valve is substantially fully closed.