94 Taurus- Pulse in variable assist power steering when turning

I've got a '94 Taurus with the optional variable assist power steering. When I turn the steering wheel I get a pulse in the wheel. It feels like the amount of 'assist' is changing. The pulse frequency is about 1 - 2 times a second. I just bought the car and it has 75k miles on it. The steering unit has a tag showing that it is a remanufactured unit. Apparently somebody else tried to fix the problem without much success.
Thanks