Power Steering Light On problems of the 2006 BMW Z4

I just purchased a 2006 Z4 3. 0i with 21000 miles from a dealership in wilmington, nc. During the test drive I noticed that the steering was unusually stiff and at higher speeds the car was somewhat hard to keep in a straight line. I dismissed the issue as a possible alignment or worn out tire issue. On the 120 mile drive home to raleigh, nc the steering became more and more erratic, pushing the car half way to the other lane. I noticed that the steering was getting really sticky and jerky the longer I drove. When trying to slightly correct the trajectory of the car to any side, the steering would not react to light torque on the steering wheel as it would with any other car I've driven before. When applying more force the steering would suddenly jump a degree or more, causing the car to oversteer and making for some rally scary and erratic maneuvers at highway speeds. When trying to correct this unexpected jump, the car would do the same thing in the other direction, causing me to swerve right and left. Later, when coming out of a long right turn on a narrow two lane road, the steering was stuck in the right turn position and suddenly popped into a left turning position, almost causing a collision with an oncoming semi truck. Since the behavior is so unpredictable and hard to control, I consider this a very serious safety issue that needs to be addressed immediately. I got lucky and I am convinced that it is only a matter of time until someone gets hurt or killed.

I have a 2004 Z4 3. 0 with 69k miles. Have had the car for several years and have noticed a steering issue that seems to be getting worse. I researched this on multiple forums and it appears that there are numerous examples of similar problems. Most relate to issues in hot tempatures, mine is more related to speed. Here are the symptoms. . . At low speeds (under 20mph) steering is very light and smooth, no issues at all. As speed increases, the steering gets heavier (as it should) but develops a "detent" at straight center. The faster the speed, the more effort needed to overcome the detent resistance, to the point that it becomes easy to oversteer the car. This can be real scary during avoidance maneuvers and quick lane changes.