I've been experience what I think is morning sickness for the past couple of weeks. Today it happened to snow about 6" and my 4Runner is now a little harder to turn and it's making a whining noise constantly.
I've read the whine is the rack and I should replace it but I've also seen instaces where people say it's the pump. What do you guys think?

99 4Runner Limited 4WD Power Steering Noise - YouTube

 

How's the fluid level?

 

I should have mentioned that the fluid level is normal.

 

You could try flushing the system to see if that helps. Make sure you use ATF and not power steering fluid.

 

I flushed the system and cleaned the reservoir filter. The power steering worked great all day yesterday and when I started it up today, all of the symptoms returned and I have no power steering now. I'm not sure why the filter cleaning would have fixed it and then it came back...

 

You might have air in the system. You could jack up the front wheels off the ground and try turning lock to lock (while it's running) to bleed the system of any bubbles. It should only take about 20 times turning the wheel back and forth slowly to get rid of the air in the system, and you should never let the fluid level get too low. I keep the cap off so I can see fluid level and if you see bubbles in it while you're bleeding, that's usually a sign that air is being evacuated from the system. Even the smallest of air bubbles can cause problems in a high pressure hydraulic system because air compresses.
If bleeding doesn't work, it's possible the pump seals could be bad. A bad rack can also cause the pump to overwork or build up too much pressure and go bad that way.

 

Update: I replaced the rack, power steering pump, PS pressure hose.

I bled the system and the power steering worked GREAT! I let the truck sit overnight and started it in the morning. The PS pump whines and after a while of driving around, I have no power steering. I'm at a complete loss. It's doing the exact same thing as it did before I replaced everything! I'm now on my second pump and cannot figure out what to do next.

I don't see any signs of leaks. The only thing I haven't changed was the fluid. I've been using cheap supertech ATF. Maybe I should flush it with some synthetic ATF. I wouldn't think the fluid would make a difference.

Also, after driving it without power steering yesterday for a few miles I parked it in the garage for a couple of hours. I came back out to look at the steering system again and started the truck up. To my surprise, I had power steering again and no noise from the pump. I didn't do anything other than let it sit. Could this be temperature related? This morning it was 20 degrees in the garage.

 

Last night I once again vacuumed the filter screen but instead of leaving it in place, I punched holes through it. Problem solved. Pump is quiet and power steering works great. I'm guessing the screen wasn't allowing the fluid to flow until the fluid was warmed up. I refilled with the same cheap fluid. I may install an inline filter but after dealing with this for almost 4 weeks, I'm going to take a break.

This was the most frustrating issue I've had with my 4Runner. At least I now have a brand new power steering system and I replaced the LBJs while I was in there.