Inter-cylinder air-fuel ratio variation abnormality detection apparatus for multicylinder internal combustion engine

摘要

A first parameter correlated with a degree of fluctuation of output from an air-fuel ratio sensor is calculated, and whether or not the calculated first parameter has a value between a predetermined primary determination upper-limit value α1H and a primary determination lower-limit value is determined. Such forced active control as reduces an air-fuel ratio shift in one of the cylinders which is subjected to a most significant air-fuel ratio shift is performed when the calculated first parameter is determined to have a value between the predetermined primary determination upper-limit value and the primary determination lower-limit value. A first parameter is calculated while the forced active control is in execution. The calculated first parameter is compared with a predetermined secondary determination value to determine whether or not variation abnormality is present.