We consider the observed aperiodic variations of S III temperature reported by ground-based observers, which take place place on time scales short in comparison with the radiation and electron collision relaxation times. We suggest that ion-ion charge exchange processes are responsible for the heating and ion-atom collisions are the source of the cooling. We attribute the fluctuations to random strong variations in the output of neutral matter from the volcanoes and surface of Io. Freshly ionized sulfur that will have near full corotation gyro-energy will undergo charge exchange with thermal doubly ionized sulfur and oxygen, thus producing hot S III. Newly injected neutral atoms can cool the ambient hot plasma by collisions on a time scale comparable to their lifetime against ionization processes. Analytic solutions of the temperature rate equations, including the time variation of the neutral and ionized matter density are found to reproduce the observed fluctuations for reasonable values of initial densities.