Originally Posted by Richard Wooldridge

I'll bet you have excessive slack in your steering gear. This will cause wandering. Test it by moving the steering wheel with the engine turned off. There should be less than 2" of play in the wheel, measured at the perimeter. You can adjust the steering gear by turning the allen screw COUNTER-clockwise a quarter turn at a time until the slop is removed. Don't turn it any further than needed to remove the play, it will cause premature wear of the gear. Also, have someone turn the wheel back and forth lightly, and check underneath to see if there's any movement in tie rod ends, etc. Replace anything that's worn. Also, check the toe-in adjustment. If it's off it can cause wandering and tire wear.