The mode coupling equations for Langmuir and ion acoustic waves are derived including an external electric field E_ext(t), nonlinear ion terms. Landau damping, and (turbulent) ion viscosity. A numerical scheme for integrating these equations shows excellent conservation of invariants and of stationary solutions for E_ext(t)=0 and zero dissipation. Numerical solutions show (a) a transient solitary wave structure ('soliton flash') 65, (b) a turbulent quasi-stationary state in which ions are heated predominantly, and (c) two kinds of relaxation oscillations depending upon the ion viscosity. Comparison with recent experiments shows qualitative agreement.