Method of determining opening of an internal combustion engine intake valve

A method of determining opening of an intake valve (10) of an internal combustion engine (1), the method including the steps of : determining the time pattern of an intake pressure (P) in an intake manifold (9) of the internal combustion engine (1), the time pattern of the rotation speed (É) of a drive shaft (4) of the internal combustion engine (1), or the time pattern of a voltage (V) at the terminals of a battery (6) of the internal combustion engine (1); determining an intake-frequency component of the intake pressure (P), the rotation speed (É), or the voltage (V); and determining opening of the intake valve (10) as a function of the intake-frequency component of the intake pressure (P), and also as a function of the intake-frequency component of the rotation speed (É) or voltage (V).