INTER-CYLINDER AIR-FUEL RATIO VARIATION ABNORMALITY DETECTION APPARATUS FOR MULTICYLINDER INTERNAL COMBUSTION ENGINE

A first parameter correlated with a degree of a variation in the output from the air-fuel ratio sensor is calculated. A possible range of a second parameter representing a degree of a variation in air-fuel ratio among the cylinders is determined based on the first parameter. The first parameter is calculated with an air-fuel ratio of a predetermined cylinder forcibly changed. A difference between the unchanged first parameter and the forcibly changed first parameter is determined. A first characteristic representing a relation between the second parameter and the difference is determined based on the possible range of the second parameter and the difference. One of the determination value and the first parameter calculated before the forced change is corrected based on inclination of the determined first characteristic.