Apparatus and method for estimating intake air flow amount of internal combustion engine

The air intake flow rate fed into the cylinder is corrected to a rate required for estimating an actual air intake flow based on the amount of change in the rate fed into the cylinder at pre-determined timings. A variance in the air intake flow rate caused by the change in the intake pressure at the portion upstream of an intake valve at a preset timing is computed based on the output of a pressure sensor. The computed air intake flow rate is added to the variance to obtain an air intake flow rate fed into a cylinder. An independent claim is also included for an air intake flow estimation method.