Simulations of nonlinear instability in a one‐dimensional Vlasov plasma with a relative electron‐ion drift velocity have been extended to parameter ranges more extensive than previously reported [Phys. Fluids28, 155 (1985)]. Linearly stable runs, withTe/Ti=1,mi/me=100, and a system length ofL=512&lgr;Dshow nonlinear hole instability. As in the case ofmi/me=4, andL=32&lgr;D, the hole depth, double‐layer potential structure, acceleration, and growth rate agree well with a theory of hole growth that results from momentum exchange from reflected particles. For a linearly unstable plasma (Te/Ti≫1), the fluctuations and their time evolution are related to the linearly stable case, but are somewhat more complex. A spatially intermittent distribution of ‘‘wavelike fluctuations’’ grows to large amplitude and then evolve into trapped ion phase‐space hole structures. The hole potentials are of ordere&fgr;/Te=1, as in the linearly stable (Te/Ti=1) runs, but becauseTe/Ti≫1, are of large amplitude (e&fgr;/Ti≫1) relative to the ions. The hole structure and dynamics agree well with the large‐amplitude extension of the smalle&fgr;/Tihole theory.