Control system for internal combustion engine

A control system for an internal combustion engine having an exhaust system provided with a catalyst, said control system comprising:

• intake air amount control means for controlling an intake air amount of said engine;
• ignition timing control means for controlling ignition timing of said engine;
• catalyst temperature rise accelerating means cooperating with the intake air amount control means for increasing the intake air amount immediately after starting of said engine and cooperating with the ignition timing control means to retard the ignition timing to make a rotational speed of said engine coincide with a target rotational speed;
• and
• lean control means for controlling the air-fuel ratio of an air-fuel mixture supplied to said engine to a lean region with respect to a stoichiometric ratio immediately after starting of said engine;
• wherein said lean control means has fuel property determining means for determining a property of the fuel being used according to the retard amount of the ignition timing controlled by the ignition timing control means during the operation of the catalyst temperature rise accelerating means, and controls the degree of making the air-fuel ratio leaner according to the property of the fuel determined by said fuel property determining means.