A dynamical equation for self-sustained and pressure-driven turbulence in toroidal plasmas is derived. The growth rate of the dressed-test mode, which belongs to the subcritical turbulence, is obtained as a function of the turbulent transport coefficient. In the limit of a low fluctuation level, the mode has nonlinear instability and shows explosive growth. The growth rate vanishes when the driven transport reaches a stationary-turbulent level. The stationary solution is thermodynamically stable. The characteristic time, by which the stationary and self-sustained turbulence are established, scales with the ion-sound transit time and is accelerated by bad magnetic curvature. The influence of the pressure gradient as well as the radial electric field inhomogeneity are quantified.