Well you are all awesome, I removed the o2 sensor completely and it runs perfect, looks like I need to take apart the exhaust this weekend. Thank everyone for all of your time and comments.

 

Before you start disassembly, which will be likely very difficult at and near the exhaust manifold (I can't remember if the pre-cat is integrated with the exhaust manifold on a third gen 99, I think they did that later)

With the vehicle not running, tap lightly with the head of a screwdriver on the bottom of the pre-cat, the cat, the resonator, and the muffler. One of them will likely sound as though it has marbles in it and or will sound very solid. It is likely the clog is there. It may be in more than one place. You can also use a back pressure tester or a vacuum gauge that also measures positive pressure check the pressures in between components. You do this by drilling a hole in the piping and threading it to match your tester. When you're done using the port, you thread in a short bolt and tighten it so there are no leaks. Whatever is clogged will show a huge pressure drop compared to the pressure before it. You can also measure the pressure at the O2 sensor bung. That will be the total effective back pressure, and by the time you find the huge pressure drop, it will drop significantly below that.

You can also disconnect the strap that holds the muffler up and see how heavy the muffler itself feels. It should be hollow. I had similar performance problems and started there. I released the clip and the pipe leading to it slammed down on the crossmember. It was heavy as hell. I just replaced it and the car ran well enough so apparently everything got blown to the back. This is why you want to check in different places before you start missing with different rusty nasty bolts and nuts.

 

Good call, I was looking at it last night and I didn't see a pre-cat on mine, but I will start sounding there and double checking. There definitely a rattle when smacking the cat conv. The cat feels super light too.

 

You can also reinstall the front O2 sensor and remove the rear one and see how it runs. What happens to the honeycomb is it will break loose and turn into a ball sometimes. I had one that ran perfect sometimes and after going around a corner it would quit running. The ball would roll around and block the output. Good plan.

 

The precat is part of the exhaust manifold on all the S-series that had a precat.

 

But if it's an S-series cars without a precat, then it won't have one, right? LOL

 

How obvious is it that I've never been under the hood of a third gen S car?

 

Here’s a 2002 DOHC engine. The precat is fairly obvious.

 

KInda sticks out like a sore thumb, doesn't it? LOL

 

Thank you.

Your power steering fluid appears to be extremely low....