Hydraulic variable valve operating apparatus and -method for uniforming the amount of intake air of different cylinders

In a multi-cylinder internal combustion engine, equipped with an electronically controlled hydraulic system for the variable operation of the engine's inlet valves (1), an indicator of the differences in the amount of air aspirated by the cylinders (20) of the engine during the respective induction phase is provided and said system controls the various inlet valves (1) of the engine in a differentiated manner, varying the time and/or opening travel for the purpose of minimizing the differences between the amounts of air aspirated by the various cylinders of the engine.