I don't know, but I've had broken tie rods that caused the same symptoms. But, for all I know, you could have a problem with the rack. Whatever it is, it isn't supposed to jerk in any direction without input from the driver and/or road surface. The shop where you had it aligned should have noticed any problems with the suspension, but you can always check. Jack up the car so one of the front wheels is off the ground. With the wheels facing straight, grab the "free" wheel at the top and bottom. There should be a little amount of play. More than that, and you got problems. Do the same thing with your hands on either side. You should get the same results. Please note that I am NOT a mechanic, unless there is a shade tree close by. Whatever, get a second opinion. Problems with Steering, Brakes, and Fuel systems should always be investigated ASAP! You don't want to become a statistic.
