Perhaps you could try using different states of your car.
Like "impact" and "pushback" or something.
So when the car first hits the forcefield you set the state "impact" and do the stuff that you want to happen with the car. Then when that stuff is finished, you set to next state "pushback" and you do that stuff you want to happen there.
You could also try the Timer behaviour.
Like when the car hits your forcefield, a timer starts, and after a certain amount of time you can trigger a "pushback"
Try to use Apply physics force towards position, or towards angle, when you want to affect your car to move in certain directions. You could also try Apply impulse to see if that gets you a better result.