Abstract: A throttle valve for an internal combustion engine in which a flow path is defined between a central core and a tube having a resiliently flexible wall, which tube separates the flow path from an adjacent working fluid chamber, whereby changes in the pressure within the chamber cause deformation to the tube wall resulting in changes in the tube cross-section between a wide open throttle position and a valve closed position, the flexible wall tube being designed to take up a valve closed position when the pressures on its opposite sides are equal, with the flexible wall tube being uniformly cylindrical in its relaxed state.