I just purchased an 2002 4.2 with 47k. The power steering works fine at low speeds but at highway speeds it gets very tight, so much so that you have to really hold the wheel firmly. It is almost as if the P S goes out entirely. Is this normal? Any help would be appreciated.
Chip

 

Your S4 has speed compensated power steering. Meaning the faster you go the stiffer the steering will be... You wouldn't be taking sharp turns at high speeds so it makes it easier to keep the car straight when going fast