1997 for explorer power steering pulsates when turning wheel

Wheels turns freely with motor off and weight off front suspension. With the
motor running the front suspension and wheels pulsate when turned either
direction. All tires are just balanced and rotated. The pulsating did not
occurr before, but dosen't matter whether it's moving or up on the hoist. Oil
level is good and no foaming is seen in the reservoir. Vehice has 132,000
miles and prior retated issues with power steering

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