1. Start-off control method for a motor vehicle using dialogue between an engine control computer and an electronically controlled mechanical gearbox when restarting the vehicle in stop-and-start mode, wherein said method comprises the following steps: verifying that a first condition is fulfilled, wherein said first condition is fulfilled when a position of an accelerator pedal is higher than a predetermined threshold position of the accelerator pedal; verifying that a second condition is fulfilled, wherein said second condition is fulfilled when the engine is in sequential injection mode; verifying that a third condition is fulfilled, wherein said third condition is fulfilled when an engine speed gradient with respect to time at instant t is higher than a predetermined threshold value based on engine speed, this third condition being called the autonomous condition; and when the first, second and third conditions are fulfilled, transmitting a start-off authorization to the gearbox.