Method of making a throttle valve housing and throttle valve housing obtained thereby

The housing is injection-molded from plastic, and has a metal cylinder (28) partially enclosed by the plastic to form the throttle aperture. An expander core (50) is pressed against the inner surface (33) of the cylinder before injection molding and partially supports it during the process. After completion of the molding, the outer periphery of the core is reduced to remove it out of the cylinder interior (70). The expander core consists of an expander unit (58) and an outer jacket (54) partially enclosing it.