Abstract: A controller for internal combustion engine includes a rotation number detecting section to detect engine rotation number and an air-fuel ratio detecting section to detect an air-fuel ratio (A/F) of air-fuel mixture and is configured to perform leaning control of the A/F. The controller further includes a rotation number difference calculating section to calculate a difference between a rotation number variation value of a worst cylinder specified as having largest rotation number variation based on the detected rotation number detected and an average value of rotation number variation values of remaining cylinders other than the worst cylinder; an estimated imbalance rate calculating section to calculate an estimated imbalance rate based on the A/F detected by the air-fuel ratio detecting section; and a lean abnormality detecting section to detect lean imbalance abnormality in a specific cylinder based on the calculated rotation number difference and the calculated estimated imbalance rate.

Abstract: A controller for internal combustion engine includes a rotation number detecting section to detect engine rotation number and an air-fuel ratio detecting section to detect an air-fuel ratio (A/F) of air-fuel mixture and is configured to perform leaning control of the A/F. The controller further includes a rotation number difference calculating section to calculate a difference between a rotation number variation value of a worst cylinder specified as having largest rotation number variation based on the detected rotation number detected and an average value of rotation number variation values of remaining cylinders other than the worst cylinder; an estimated imbalance rate calculating section to calculate an estimated imbalance rate based on the A/F detected by the air-fuel ratio detecting section; and a lean abnormality detecting section to detect lean imbalance abnormality in a specific cylinder based on the calculated rotation number difference and the calculated estimated imbalance rate.

Abstract: A controller includes an exhaust gas recirculation (EGR) system for performing EGR control, the system including an EGR passage for recirculating exhaust gas per cylinder and an EGR device for controlling a flow rate of the exhaust gas to be recirculated. The controller is arranged to perform internal combustion engine by learning control of an air-fuel ratio (A/F) during the EGR control. This controller includes a blocking determination section including first and second determination sections to determine blocking of the EGR passage in a specified cylinder. The blocking determination section is configured so that the first determination section makes preliminary determination of blocking of the EGR passage and the second determination section makes main determination of blocking of the EGR passage.