Code:
function up() {
	var i = 0;
	while(height <= 1531 && !key_x &&  !key_x) {
		i += 0.1*time_step;
		i = clamp(i,0,2);
		height += i*time_step;
		wait(1);
	}
}


i geus you want to control it white the keys:
w = up
s = stop
x = down

and

Code:
height = height;

wont make any sense because the while loop is still running and 1=1 and 2=2 so it get increased every frame

"empty"