We study the dynamical localization in the system of a two-level Rydberg atom interacting exactly with a pulsed standing microwave. This system approaches an atom optics realization of usual delta-kicked rotor under the rotating-wave approximation (RWA). We find that the non-energy-conserving processes neglected in the RWA have a strong effect on the classical and quantum diffusion, which, compared with the results of the RWA, can enhance, reduce and even completely suppress the momentum diffusion under certain kicked conditions.