The steering wheel jitters back and forth when I'm idling the car and steering. I do have a minor idle issue where the idle speed drops a little low, but I don't remember it affecting the wheel. Should I purge the power steering system, just fill with new fluid or is this a bit more serious?

My car is a 740 turbo 89 model year.

 

These power steering systems are self purging. Turning the wheel lock to lock a few times while idling will purge the system when it has been opened for service. My guess is either the p/s belt is loose orthe pump is on its way out. Do make certain the pump is to the full mark.

 

Well, it's back to normal. So I guess it purged itself like you said it would do.