An engine control device is configured to prevent a rotational speed of a vehicle engine from becoming abnormally low during deceleration due to an abnormal air-fuel ratio. When conditions for feedback control of engine idle speed are not satisfied and self diagnosis results of the air-fuel ratio control system are normal, the control device determines if the air-fuel ratio is in an abnormally lean state. The control device then determines if the abnormally lean air-fuel ratio state has continued without interruption for a prescribed period or longer. If so, the control device calculates an air-fuel ratio abnormality compensation quantity, e.g., adds an air-fuel ratio abnormality compensation value to an idle compensation air quantity, to increase the intake air quantity and compensate for the engine torque deficiency resulting from the lean air-fuel ratio state.