I have an ED, 6cyl auto, and my steering is perfect at slow speeds. You really shouldn't be turning the wheel while your car is stationary(dry steering), as it is no good for the steering. I have had the power steering pump die on me, but b4 it did and after it was replaced the steering has been good. When it was on the way out, the steering was roo's brother ted, making a noise and vibrating like yours. Turns out tho that for a dodgy fix for a buggered power steering pump is to relax the tension on the belt a bit. It will do what yours is doing but you won't have to pay for a new pump for a little while. As soon as the belt on mine was set at the correct tension when it was stuffed, it snapped a new belt. Was lucky tho cos i got my car from a yard it had a warranty which covered this. Saved me $200 odd bucks
White ED falcon, 2.5" redline zorst, pacemakers, 1 muffler, hi-flow cat, XH snorkel and K&N filter, 17" wheels, clear side and front indicators, king springs (low).