Abstract We have performed self-consistent 2.5-dimensional nonsteady MHD numerical simulations of jet formation as long as possible, including the dynamics of accretion disks. Previous simulations showed that, in the case where the calculation time of the simulations is very short as compared with the time scale of observed jets, there is no significant difference between the characteristics of the nonsteady and steady MHD simulations. Thus, we have investigated long-time evolutions of the mass-accretion rate, mass-outflow rate, jet velocity, and various energy fluxes. We found that the ejection of a jet is quasi-periodic. The period of the ejection, $T_{\rm ejection}$, is related to the time needed for the initial magnetic field, $B_0$, to be twisted to generate a toroidal filed, $T_{\rm ejection} \propto {V_{\rm A}}^{-1} \propto {B_0}^{-1} \propto {E_{\rm mg}}^{-1/2}$, where $V_{\rm A}$ is the Alfvén velocity and $E_{\rm mg}$ the initial magnetic energy. We compared our results with both the steady-state theory and the previous 2.5-dimensional nonsteady MHD simulations. We found that the time-averaged velocity of the jet, $V_{{\rm jet}, \mathrm{avg}}$, is $\sim 0.1V_{\mathrm{K}}$ and $\sim 0.1V_{{\rm jet}, \mathrm{max}}$, where $V_{\mathrm{K}}$ is the Keplerian velocity at $(r,{z})=(1,0)$ and $V_{{\rm jet},\mathrm{max}}$ the maximum velocity of the jet. Nevertheless, the characteristics of our simulations are consistent with those of the steady solution and previous short-time simulations. We found that the dependences of the time-averaged velocity and the mass-outflow rate, $\dot{M}_{{\rm w},\mathrm{avg}}$, on the initial magnetic field are approximately $V_{{\rm jet},\mathrm{avg}} \propto {B_0}^{0.3}$ and $\dot{M}_{{\rm w},\mathrm{avg}} \propto {B_0}^{0.32}$, respectively.