Before I begin, I would like to thank all who have replied to my questions here at the Cherokee forum.
My 98 xj is idling a little rough at about 800 rpm.No missing detectable by sound or feel when accelerating. I have read a few posts here that have a similar problem.
I took it to autozone for a scan last week and it came out a 138 code which had something to do with bank 1 lean and an 02 sensor,
I lost the printout and went back this morning and the new scan was a 171 which concerns low fuel pressure. I thought to change the fuel filter as a starter.NAPA shows only a filter/regulator combination. Rock auto has bot a cartridge type and the filter/regulator. OK, now this is the embarrassing part of my post. I just crawled under the jeep to see what type I need and could not find the thing. It appears a fuel line is running to a black box with a few other lines leaving and going to the front. I really did not want to remove anything until I felt sure about it. Any ideas?

 

Don't feel too bad about not find it. This is the fist vehicle I have owned that did not have an easily replaceable fuel filter. I was stumped the same way you are. The filter is part of the fuel pump and should be about the last place you look.
Those codes point towards your O2 sensors. If this XJ is new to you, here is a good starting point.
Invest in a code reader. You can get one for under $50 from Amazon. will save you a lot of time and hassle.
You can also get a Bluetooth enabled one and record data. If you have an intermittent O2 sensor problem, that would find it.
You may also want to check your fuel pressure with a rented gauge. It should read ~49psi at the fuel rail. If that's good then look elsewhere.

 

Testing fuel pressure is the first thing I would do if your XJ was in my garage. If you don't have a fuel pressure gauge, you can often rent them from your local parts store. Call around for availability.

The fuel pressure spec for your 98 is 49 psi, plus or minus 5 psi.

Start there. Post up what you find. And I agree that you should invest in a tool to read codes. A simple code reader can be had for under $40. A scan tool which gives you a lot more options to pull data will cost you more but may be worth it. Snoop around on Amazon. Innova and Equus makes great code readers and scan tools.

Good luck, keep us posted!

 

Plugs are gaped .035? Rough idle is what reminds me I forgot to do that!