Abstract: A control system and method for an internal combustion engine in which an intake air pressure sensor of semiconductor or strain gauge type arranged in an intake manifold is used to detect the intake air pressure at a timing at or after bottom dead center during the intake stroke, the timing being detected by detection of a predetermined crank angle at or after bottom dead center or the zero of intake air flow rate. Operating conditions of the internal combustion engine are controlled early by an air pressure detection signal. For example, the air-fuel ratio of the mixture gas before combustion is estimated to control the ignition timing.