Method for generating a command signal (Ei) for the value of idle speed for a combustion engine of a tractor, said method comprising the steps of: a) providing a control unit comprising a processor; b) receiving a transmission fluid temperature signal (To) which is related to the temperature of the transmission fluid of the transmission group of the tractor, and receiving a cooling fluid temperature signal (Tc) which is related to the temperature of the cooling fluid of the engine of the tractor; c) receiving a tractor speed signal (Vtr) on the control unit, said tractor speed signal (Vtr) relating to the speed of linear movement of the tractor; on the processor: d1) after receiving the cooling fluid temperature signal (Tc), if the cooling fluid temperature signal (Tc) is lower than a cooling fluid temperature threshold (Tcth), selecting a first value of idle speed as a function of the cooling fluid temperature signal (Tc), said first value of idle speed being greater than a nominal idle speed value (Ein) of the combustion engine; d2) after receiving the transmission fluid temperature signal (To), if the transmission fluid temperature signal (To) is less than a transmission fluid temperature threshold (Toth), selecting a second idle speed value as a function of the transmission fluid temperature signal (To), said second idle speed value being greater than the nominal idle speed value (Ein); d3) if the tractor speed signal (Vtr) is not zero, selecting a third idle speed value as a function of the value of the tractor speed signal (Vtr), said third idle speed value being greater than the nominal idle speed value (Ein) of the combustion engine; e) calculating the desired idle speed value (Eid) as the maximum value between the first, the second and the third idle speed value; on said control unit: f) generating a command signal (Ei) for the idle speed value for the engine as a function of the desired idle speed value (Eid) calculated on the processor in step e). a) providing a control unit comprising a processor; b) receiving a transmission fluid temperature signal (To) which is related to the temperature of the transmission fluid of the transmission group of the tractor, and receiving a cooling fluid temperature signal (Tc) which is related to the temperature of the cooling fluid of the engine of the tractor; c) receiving a tractor speed signal (Vtr) on the control unit, said tractor speed signal (Vtr) relating to the speed of linear movement of the tractor; d1) after receiving the cooling fluid temperature signal (Tc), if the cooling fluid temperature signal (Tc) is lower than a cooling fluid temperature threshold (Tcth), selecting a first value of idle speed as a function of the cooling fluid temperature signal (Tc), said first value of idle speed being greater than a nominal idle speed value (Ein) of the combustion engine; d2) after receiving the transmission fluid temperature signal (To), if the transmission fluid temperature signal (To) is less than a transmission fluid temperature threshold (Toth), selecting a second idle speed value as a function of the transmission fluid temperature signal (To), said second idle speed value being greater than the nominal idle speed value (Ein); d3) if the tractor speed signal (Vtr) is not zero, selecting a third idle speed value as a function of the value of the tractor speed signal (Vtr), said third idle speed value being greater than the nominal idle speed value (Ein) of the combustion engine; e) calculating the desired idle speed value (Eid) as the maximum value between the first, the second and the third idle speed value; on said control unit: f) generating a command signal (Ei) for the idle speed value for the engine as a function of the desired idle speed value (Eid) calculated on the processor in step e).