A method for controlling operation of a power unit group of a vehicle including at least one driving engine, a manual gearbox with plural gears and a clutch, in which a control system with a computer determines the target power to be supplied by the power unit group depending on information corresponding to an intention of the driver and displayed on an input of the computer. During a gear change, the information on the driver's intention is frozen during the clutch opening time so that the control system does not take into account a potential disturbing information, such as a quick foot release, displayed on the input between the clutch opening moment and the clutch closing moment to determine the target power to be supplied. The method can be applied particular to a manual gearbox having a system for displaying the recommended gear ratio on the dashboard.