There is described a method and an apparatus for use with the fuel preparation system of an internal combustion engine, for example, a fuel injection system which operates injection valves with electrical control pulses. When the gas pedal of a vehicle is actuated abruptly, the air flow measuring device of such systems is subject to oscillations around its equilibrium point, and the initial one of these swings is used to cause enrichment of the fuel-air mixture. The return swing generates an undesired lean signal which is suppressed by a "damping circuit". In addition, there is provided mixture enriching during steady applications of the gas pedal by means of a time-decaying enrichment signal generated by a slow acting circuit which operates in superposition to the action of the damping circuit. Both circuits may be suppressed by a blocking circuit during certain engine conditions, for example, during engine starting and engine overrunning as well as on the basis of temperature.