Abstract: An improvement in internal combustion engines of the type having an air supply line for supplying air to a combustion chamber and an auxiliary air valve containing a valve member connected to and movable with a membrane which is displaceable under action of the suction pressure in the air supply line includes, in a further embodiment, a valve line interconnecting the air supply line and one side of the membrane, a condition-responsive valve located in the valve line which is shiftable from a first position communicating one side of the membrane of the auxiliary air valve with the atmosphere and a second position communicating the one side of the membrane with the air supply line, and wherein the condition-responsive valve is shifted between the first and second positions for opening the auxiliary air valve during starting of the engine and for closing the auxiliary air valve during the warm operating phase of the engine.