Power steering problems. 98 Tacoma

Power steering had been talking to me for several weeks. Last week it was still making noise but no or greatly reduced power steering at low rpms. Oil is very dirty. Purchased new pump and put it on back seat of truck. Next day power steering started to work a little. Next day works fine and no more noise. Has anyone had this problem and could it be the dirty fluid and all I need is to flush

 

i had almost the same thing happen. no power assist. next day while out wheeling i hit a bump. and rubbed the steering wheel a bit. gave her a kiss and she has worked ever since.