Control system for internal combustion engine

A control system for an internal combustion engine, which is capable of properly determining timing for restarting the engine in a stopped state when idle stop control of the engine is executed during a heating operation of an air conditioner, thereby making it possible to ensure marketability and fuel economy performance in a well-balanced manner. The control system executes the idle stop control of the engine during the heating operation of the air conditioner. The control system includes an ECU. The ECU sets a lower limit blowout temperature, calculates an estimated blowout temperature, and controls the engine such that the engine is restarted when the estimated blowout temperature has become not higher than the lower limit blowout temperature.