A lower intake manifold assembly includes a lower housing and a runner insert fitted into the lower housing. The lower housing may be made of metal and the runner insert may advantageously be made of a synthetic resin material. The runner insert provides a sealing surface between the lower housing and the cylinder head of an internal combustion engine. The runner insert also supports a charge motion control valve flap assembly that advantageously may include a shaft and synthetic resin flaps over-molded onto the shaft.