You could have chassis tweak caused by an impact (the mr4 series has this problem) To help solve this issue you take off the wheels and loosen the chassis screws at the stiffeners, push down on the chassis when placed on a flat surface and retighten the screws. The other problem it could be is the servo saver machanism built in to the steering rack. It occasionally loosens and gives the problems you described. Just tighten it back up to the manual specs, you may want to add a drop of loctite to the screw and you're set. Or you could have damaged the servo or steering machanisms in some fom. I would check it all thoroughly.--Al