maps is established to be large on the other hand when the engine becomes warm the value of the air fuel ratio correction volume is kept small and the volume differences between each of the plurality of maps is established to be small the control unit 12 detects a surge torque level which is responsive to changing of the initial air fuel ratio correction volume at the time of engine starting and the suitable operating conditions discriminating means is responsive to change the data map to be utilized in response to changing of the air fuel ratio correction volume as will be explained in detail hereinbelow with reference to the flowchart of fig3 at a first step s1 of the steps carried out according to the system of the invention every cycle of a preselected small unit of time i e 12 8 u03bcs the combustion pressure value output by the sensor 11 as an analog signal is converted to a digital signal then at a step s2 the combustion opening at the drive stroke of each cylinder is read based on the output of the crank angle sensor for determining if the crank angle is within a predetermined crank angle range if a crank angle within the predetermined range is not detected.