We perform a rigorous analysis of the quasineutral limit for a hydrodynamical models of viscous plasmas represented by the Navier Stokes Poisson system in 3-D. A common feature of this kind of limits in the ill prepared data framework is the high plasma oscillations, namely the presence of high frequency time oscillations of the acoustic waves. Moreover and other issue which makes the limiting behaviour analysis very hard is the presence of very stiff terms due to the electric field. We shall provide a detailed mathematical description of the different behaviors of the various vector fields acting in our system, what and which are the relationship between high frequency interacting waves, dispersive behavior and the different roles of time and space oscillations.