Control device for internal combustion engine and control method for internal combustion engine

A control method for an internal combustion engine including a plurality of cylinders, a fuel injection valve configured to supply fuel to each cylinder, an exhaust gas recirculation passage configured to connect an exhaust passage and an intake passage, an exhaust gas recirculation valve configured to adjust a flow rate of exhaust gas flowing from the exhaust passage into the intake passage through the exhaust gas recirculation passage, and an air-fuel ratio sensor provided in the exhaust passage, the control method comprising:

• executing, by an electronic control unit, determination processing for determining that a degree of imbalance abnormality is greater when a fluctuation amount of a detection value of the air-fuel ratio sensor is relatively large than when the fluctuation amount is relatively small, the degree of imbalance abnormality being a degree of variation of an air-fuel ratio in a combustion chamber of each of the cylinders when the fuel injection valve is operated to control air-fuel ratios in the cylinders to be equal to one another;
• and
• in the determination processing, determining, by the electronic control unit, that the degree of imbalance abnormality is smaller when an exhaust gas recirculation rate is relatively small than when the exhaust gas recirculation rate is relatively large even though the fluctuation amount is the same, the exhaust gas recirculation rate being a value obtained by dividing an amount of exhaust gas flowing from the exhaust gas recirculation passage into the intake passage by an amount of air flowing into the intake passage.