The cyclic control pulses for actuating the fuel injection valves of an internal combustion engine are extended during engine starting at low temperatures. The degree of pulse extension, i.e. of fuel enrichment, is made dependent on engine temperature and decreases as a function of cranking time. In addition, a repeated starting attempt will be accompanied by reduced pulse extension to prevent excessive enrichment of the mixture. The pulse extension may also be retained for a period of time after engine cranking to insure smooth running.