This might not all apply to the Z system/parts etc.
Power steering troubleshooting guide
Steering wheel surges or jerks
1. low power steering fluid level
2. loose pump drive belt
3. weak pump pressure
4. stickingflow control valve
Excessive play in steering wheel
1. air in hydraulic system
2. incorrect steering gear adjustment
3. loose steering gear coupling
4. loose steering shaft universal joint
5. faulty rotary valve
Poor return of steering wheel
1. maladjusted steering wheel
2. dry ball joints or linkage joints
3. binding ball joints or linkage joints
4. incorrect front wheel alignment
5. maladjusted hweel bearings
6. kinked return hoses
7. internal pump leakage
8. contaminated power steering fluid
9. mis-aligned steering gear to steering column
10. tight steering shaft bearings or bushings
11. bent or damaged rack
12. sticking or plugged spool valve