An electronic engine controller (EEC) controls the delivery of fuel to an internal combustion engine via one or more fuel injectors by executing a background routine to measure a plurality of system conditions including airflow and engine temperature. A response value is generated as a function of an aircharge value, the temperature value and a valve effect value. The EEC detects an interrupt which occurs prior to combustion of an air/fuel mixture within each combustion chamber of said engine, and in response to the interrupt execution of the background routine is halted and a foreground routine is executed in which the airflow is measured, an updated aircharge value is generated and the response value is updated as a function of the difference in aircharge values and a predetermined response alteration value. The aircharge value is replaced with the updated aircharge value. A base fuel injector signal, generated by known methods, is modified by the response value, and execution of the background routine is restarted upon completion of the foreground routine.