How do I get to my Upstream 02 sensor

I been having some Idle problems, I think it may of been a combination of things.

I got a cel "P0171" which could be fuel pressure, Oxygen Sensor defective, Iginition misfire or fuel injector problem according to the code reader.

I changed my TPS and that helped with the idle racing at lights occasionally. (fixed)

I ran the BG44 fuel injector kit though the jeep.
I cleaned the throttle body and IAC.
I put on new plugs, wires, rotor, cap.

But the idle is still slightly off, it just is not that smooth, like it has a slight sputter. And I believe my gas mileage is gone down.

After researching the board it seems like some who have had the same exact problem and code changed out the upstream 02 sensor and fixed to the problem.

I think it is right before the cat but I never changed it before, does anyone know exactly where it is.

Thanks for the help.

Sorry I have a 1999 4.0 XJ.

It should be in the collector of the exhaust manifold, just before the downpipe flange. You'll need an oxygen sensor socket to get it out (it's an extra-deep 7/8" socket with a slot milled in one side to pass the wiring.)

Get a new sensor from Bosch or AC Delco (which is probably a reboxed Bosch anyhow.)

Remove the old sensor with the manifold still a little warm - it will be easier.

Apply never-seez to the threads on the new one (if it doesn't already have some on,) and torque to 19-21 pound-feet only. Yes, use a torque wrench. Yes, doing so will save you trouble, time, and money next time you have to change the thing.

I forgot to mention my gas mileage has gone down also, so with the "p0171" code, it should be the upstream 02 sensor, because doesn't that sensor control the air fuel mixture?

This is a tough one, I guess I'll give it a try, I can't thing of anything else at this point.