Abstract: A sensing means is provided to monitor combustion of fuel and air supplied to an internal combustion engine, for example by sensing ignition pulses, combustion pressure, or cylinder temperature. Signals, as sensed, are compared and if one of these signals is extreme with respect to an average and, at the same time, the temperature of a catalytic reactor in the exhaust system becomes excessive, supply of the combustible fuel-air mixture to the specific cylinder is interrupted. To permit starting with unequal heating of cylinders, interruption of supply of the combustible fuel-air mixture is cancelled during starting, as sensed, for example, by closing of the starting switch, or low temperature in the engine system.