Abstract: The invention provides an abnormal inter-cylinder air-fuel ratio imbalance detection apparatus for a multi-cylinder internal combustion engine. The abnormal inter-cylinder air-fuel ratio imbalance detection apparatus is provided with: an air-fuel ratio sensor provided at an exhaust passage of the multi-cylinder internal combustion engine; an abnormal imbalance detection portion that detects an abnormal imbalance between air-fuel ratios corresponding to respective cylinders of the multi-cylinder internal combustion engine through a comparison between a value of a parameter correlative to a variation of an output of the air-fuel ratio sensor and a predetermined abnormality threshold; and a correction portion that corrects at least one of the value of the parameter and the abnormality threshold based on an atmospheric pressure.

Abstract: When EGR is on (YES in S1OO), an ECU selects a first map for the time when EGR is on as an intake air temperature correction map (S 102). Thus, an intake air temperature correction retardation amount ? is set to an intake air temperature correction retardation amount ?on (THa, KL) for the time when EGR is on, which corresponds to an intake air temperature THa and an engine load KL. On the other hand, when EGR is off (NO in S1OO), the ECU selects a second map for the time when START EGR is off as an intake air temperature correction map (S 104). Thus, the intake air temperature correction retardation amount ? is set to an intake air temperature correction retardation amount ?off (THa, KL) for the time when EGR is off, which corresponds to the intake air temperature THa and the engine load KL.