Several things you should check. You need to get the wheels off the ground. Jack stands or a lift. First check your wheel bearings for play with your hands at 12 and 6 o clock. Then move your hands to 9 and 3 o'clock and check your tie rods inner and outer. If you find some play in what looks like the inner tie rod you should pull the boot off the steering gear and check the gear itself. The shaft the tie rods thread into can get loose in the rack itself. When that happens the rod will move up and down in the bushings. That presents itself as loose steering feel.
So the other thing is a solenoid that mounts on the steering rack near the drivers side. That solenoid changes between not much assist for going 70 mph and max assist for parking lot maneuvers. If it gets stuck at max assist and your going 70 mph,your going to feel like your making a lot of corrections to go straight down the highway. I've seen them broken right the fuck off and have no warning lights on. Just a heavy steering complaint, or on the flip side what your describing.