Control apparatus and control method for internal combustion engine

A control apparatus for an internal combustion engine, the control apparatus being configured to execute an air-fuel ratio control based on an output of an air-fuel ratio detector provided in an exhaust passage through which exhaust gas from a plurality of cylinders flows, the control apparatus comprising:

• an abnormal lean deviation detection portion configured to detect whether an abnormal lean deviation is occurring in at least one specific cylinder among the plurality of cylinders, the exhaust gas from the at least one specific cylinder influencing the air-fuel ratio detector more strongly than the exhaust gas from each of a rest of the plurality of cylinders;
• and
• an enriching control portion configured to execute an enriching control for the at least one specific cylinder when the abnormal lean deviation detection portion detects that the abnormal lean deviation is occurring in the at least one specific cylinder;
• wherein the abnormal lean deviation detection portion detects whether the abnormal lean deviation is occurring in the at least one specific cylinder based on a change in engine revolution speed at a time of cold engine start or a value that represent the change in the engine revolution speed at the time of cold engine start.