Method of acquisition and processing of an intake pressure signal in an internal combustion engine without an intake manifold; the internal combustion engine having at least one cylinder that receives fresh air through an intake duct, which is controlled by a butterfly valve and is provided with a pressure sensor connected to an electronic control unit. The acquisition and processing method provides for the following steps: measuring, via the pressure sensor, the instantaneous induction pressure at a plurality of different crank angles distributed over an engine cycle; storing, during each engine cycle, the instantaneous induction pressures in a fast acquisition buffer of the electronic control unit; and determining, at the end of each engine cycle, the mean induction pressure in the engine cycle by calculating a mean of the instantaneous induction pressures previously stored in the fast acquisition buffer of the electronic control unit.