Fuel supply amount control apparatus and method for internal combustion engine

A fuel supply amount control apparatus for an internal combustion engine uses an idling control amount QISC obtained by reducing an idling control amount Qa by an idling control amount correction value KQISC, when determining the amount of fuel injected for the lean combustion when the vehicle is running. Therefore, during the lean combustion with the D range is selected, there is substantially no difference between the road load amount of fuel injected during the idling state and the road load amount of fuel injected during a low-speed running of the vehicle. Hence, an increase in the amount of fuel injection during the low-speed running of the vehicle based on the lean combustion achieved upon a fuel increase request does not result in an excessively great output torque of the engine, so that the low-speed running of the vehicle becomes stable and good drivability can be maintained.