A control system for an internal combustion engine that performs learning of a throttle opening degree during idle operation, at which a target idle speed can be obtained, the control system comprising a control section that is configured to use a first learned value and a second learned value as learned values of the throttle opening degree during idle operation and to update the first learned value when a state of combustion is not deteriorated, and update the second learned value when the state of combustion is deteriorated.