The transport of ions inward from Io's orbit is first modeled on the assumption that radial diffusion is the dominant transport mechanism and then modeled with a combination of diffusive and convective transport. Included in the model are thermal as well as number density transport, radiation, ionization and pickup of local neutrals, recombination, charge exchange, and Coulomb interactions. Pure diffusive transport is capable of accounting for the dramatic inward depletion of the torus only by invoking recombination or by postulating a massive increase in the production rate of torus ions sometime prior to Voyager encounter. It is shown that radical time dependence (it is necessary to increase the source strength by a factor of >20 before the arrival of Voyager) cannot account simultaneously for the density and temperature observations. Similarly, recombination is found to be much too slow to be the cause of the observed density decrease inside of Io. The model combining convection and diffusion can reasonably match the data, but only with a diffusion coefficient 100 times less than that derived from Pioneer observations. It is shown that the Pioneer derived diffusion rate combined with Voyager temperature and density measurements imply a large non-radiative sink of energy in the inner torus.