In an engine control valve having a body delimiting an internal duct and including a flap mounted such that it can pivot via a spindle of the flap, the flap includes a first part and is able to pivot between an open position that allows gases to pass along the duct, and a closed position in which the flap comes into contact with a flat seal inserted between two elements of the valve body, the seal has an exterior contour that externally surrounds the exterior contour of the flap, the seal includes an opening and a solid portion, the first part closes off the opening of the seal when the flap is in a closed position, and the seal includes at least one slit formed in the peripheral zone of the solid portion, the at least one slit communicating with the opening.