We have investigated the reaction of ammonia ions with methane molecules (CD4) over the collision energy range of 0.5-10.0 eV and for ammonia ion vibrational states ranging from nu(2)=1-10. Under these conditions, the two main product channels are NH3D+ and CD3+. The cross section for formation of NH3D+ is enhanced with increasing internal energy at collision energies below 6.0 eV, and independent of internal energy at higher collision energies. The enhancement is greater for forward-scattered products indicating that ammonia-ion vibrational energy enhances reactivity at large impact parameters. The mechanism for formation of CD3+ involves collision-induced dissociation of CD4 (or NH3+) which leads to the formation of a short-lived [NH3CD3](+) ([NH2CD4](+)) complex, which then decays to products. This reaction is found not to be vibrationally mode selective, which is consistent with the hypothesis that mode selectivity in reactions of ammonia ions is driven by the Franck-Condon overlap whenever charge transfer is involved.