hi i'm just starting a car project using GS physics.. here's the first 2 lines of code and its already going crazy

////code start
action car_move()
{
//all the standard settings
phent_settype(my,PH_RIGID,PH_BOX);
phent_setmass(my, 30, PH_BOX);
phent_setfriction(my, 15);
phent_setdamping ( my, 10, 20 );
ph_setgravity( earthgravity );
phent_enable(my, 1 );
while(1)
{
camera.x = my.x-200*cos(my.pan); camera.y = my.y-200*sin(my.pan); camera.z = my.z+50;
camera.pan = my.pan;
my_pos[0]=my.x; my_pos[1]=my.y; my_pos[2]=my.z;
//heres the force vector for_force which gives a force along the car's local X-axis
if(key_cuu){for_force[0]=1000;} else{for_force[0]=0;}
if(key_cul){for_force[1]=500;} else{for_force[1]=0;}
phent_addforcelocal(my,for_force,my.x);
wait(1);
}
}
////code end
only this much so far.. but it isn't working
it works well initially and the car goes forward until i press the left key and it turns.. after the turn if i press the up arrow key it just spins on the ground instead of going forward.. i'm using 'addforcelocal' so it should give the force along the local 'x' axis.. i don't know why it gives something like a torque..