Here is the experience I had with losing the power steering pump fluid on an RX4 2.0 litre petrol LHD (year 2000) due to never really paying attention to what level it was at !
Going down drive-way and then on curve noticed that suddenly the steering started to get these stiff spots when rotating the steering wheel. A bit like when you rotate an electric motor and you feel these easy and then hard bits as it rotates past the magnets - a smooth resistance. Checked fluid and it was empty !.
D'oh !. Can't remember last time I checked. One of those things. Every other fluid I check but....
Didn't have any fluid but got the car backwards up the driveway and then checked Internet for what fluid type. AGIP ATF II D (which I found on the Internet on a dealer lubricants sheet). Used bike to go buy some fluid. Topped up and then did a few full lock- to lock turns but still had these hard spots. Nothing really bad - like driving an old Landrover.
Also when you open the PS fluid reservoir (located to the front near the radiator) then it has a black tubular insert (3cm diameter by around 8 cm deep) . This slides up and out. It is an anti-splash baffle with a filter mesh on the bottom. This may have a very fine sludge on it (mine did). I used new fluid to clean this off.
Ran it down the road and around the block but still not right. It basically took around 20-30 kilometers of slow windy roads and at least 1 week for it to get rid of whatever air had got in and get back to normal. Have run it for 300 kms since then (around 2 weeks ago) and no problems. Fluid levels OK so it was just my lack of attention but it's not catastrophic.