INTERNAL COMBUSTION ENGINE ABNORMALITY DIAGNOSIS DEVICE

A diagnosis device is intended for an internal combustion engine including a supercharger, a blow-by gas passage that communicates between a portion of an intake passage and a crankcase, a PCV pressure sensor that detects a PCV pressure in the blow-by gas passage, and a crankshaft. The device executes specifying a specific period for which the amount of fluctuations in the intake air amount per unit time is a prescribed value or more on condition that the intake air amount is a determination air amount or more, calculating the amount of fluctuations in the PCV pressure during the specific period, and determining, based on the amount of fluctuations in the PCV pressure, the presence of an abnormality in the blow-by gas passage. The device sets the determination air amount to a smaller value when the rotational speed of the crankshaft is high than when the rotational speed is low.