The invention relates to an internal combustion engine comprising a fuel injector (2) for each cylinder; a fuel injection control unit (4) for controlling fuel injection quantity and a piston (5) in each cylinder whose compression action causes a mixture of air and fuel to be ignited. The engine is further provided with inlet and outlet valves (6, 7) and various sensors (12 16) for measuring various engine operating parameters. During compression ignition mode, the control unit (4) is arranged to select a .lamda.-value from a map stored in the control unit, which value is a function of engine load and engine speed, and to compare the actual .lamda.-value with the selected .lamda.-value; whereby the control unit is arranged to adjust the intake manifold pressure as a function of the difference between the said .lamda.-values in order to obtain the selected .lamda.-value. The invention further relates to a method for operating the engine and a computer readable storage device (4).