In an electronic engine control system for an internal combustion engine, in which a cylinder air mass flow rate to be actually introduced into an engine cylinder is calculated using measured value of a parameter associated with engine operating condition, and a fuel injection amount is controlled corresponding to the calculated cylinder air mass flow rate, a method for calculating the cylinder air mass flow rate comprising the steps of:
- deriving a mass flow rate of a recirculated exhaust gas flowing into an induction passage of the engine, said engine having an exhaust gas recirculation system;
- estimating a partial pressure of the exhaust gas within said induction passage on the basis of said mass flow rate of the recirculated exhaust gas;
- and
- deriving said cylinder air mass flow rate on the basis of the estimated value of the partial pressure of the recirculated exhaust gas.