The ion temperature gradient driven drift mode turbulence (ηi mode) has been studied with a fully toroidal fluid model. The saturation amplitudes and ion energy transport have been obtained by numerical simulations. An analytical model for mode coupling saturation in combination with a quasi-linear approximation has been used to derive a simple diffusion coefficient which is in good agreement with the simulations. The scaling of the diffusion coefficient χI with Ln/LB indicates a considerably improved agreement with the experimental radial variation, and the scaling with Te/Tj has been found to favour tokamak operation in the hot ion regime. The diffusion coefficient is consistent both with the improved confinement for pellet injection experiments and with the H-mode results for very large ηi.