How to simulate a transition with noise using the stoch_simul command (Dynare)?

transition.mod

var y;

varexo e;

parameters rho, sigma, ybar;

ybar = 2;
rho = .99;
sigma = .01;

model;
    y = (1-rho)*ybar + rho*y(-1) + sigma*e;
end;

shocks;
var e; stderr 1;
end;

histval;
y(0) = 0;
end;

stoch_simul(order=1,periods=500,drop=0);

plot(y);