it will be noted that the two types of action are not equivalent in one case the control of the compressor 12 differs for a time equal or approximately equal to the period of the initial opening and closing of the butterfly valve 1 while in the other case the 34 rebound 34 phenomenon is actually anticipated by causing the reclosing and reopening of the butterfly valve 1 at a selected instant in relation to that of the actual control of the compressor 12 it will also be noted that in the example described there is a coincidence between the end of the initial action on the butterfly valve 1 the actual control of the compressor 12 and the beginning of the counteraction compensating for the 34 rebound 34 however the invention is not limited to this embodiment and a time lag can also be provided between the action and the counteraction and the actual control of the compressor 12 also may not coincide with the end of the initial action of the butterfly valve 1 we will now refer to the tables below which show the test results obtained without regulation tables 1a and 1b and with full regulation tables 2a and 2b and in which it is apparent from these tables that the regulation according to the invention makes possible a significant reduction in the variation of engine speed mainly at low idling speeds on the other hand this regulation makes possible a significant reduction of the time for returning to the nominal speed especially in the case where the hydraulic converter of the automatic transmission is engaged it is important to note that the physiological sensations of the occupants of the vehicle are notably improved indeed.