Actually, it bogs down at lower rpms - regardless of whether its idling or in gear.

Plugs/wires/cap replaced about 3-4 months ago.
Rear o2 sensor (after cat) replaced about 2 months ago.

I bought the front o2 sensor shortly after I replaced the rear but never got around to installing it. Started having some rough idle issues and the CEL came on, so I installed the front o2 sensor the other day. The CEL went away, but still having similar bogging down issues. Again its when idling or at lower rpms.

Does the onboard cpu need to reset itself with the new o2 sensor? (I didn't think that was the case when I replaced the rear)

Should I run some seafoam through it again? Is there something else I'm missing??

 

Check and clean your IAC.

 

Do this and run some injector cleaner like Seafoam, Lucas fuel treatment, etc. Also clean your throttle body and replace your fuel filter. Is your air filter clean?

Did you make sure that the plugs were gapped correctly? Also, double check that you have the firing order correct

 

Picked up Seafoam today and will do this tonight. Did this a little over a year ago and it seemed much peppy-er after. Also will look at throttle body cleaning.

Plugs and wires have been working fine since changed, just noticed issue in the past week. Actually I checked and I did my Cap/wires a few months back but the plugs themselves were actually done about a year ago. I would think should be good for more than one year (7500 miles) though...

Fuel filter is a pain to change (have to take tank off), right??

 

Oh okay wires should be fine then. And scratch the fuel filter. I didn't see what year your XJ was because I was on the mobile app at the time. With your 99, the fuel filter is inside the gas tank, part of the fuel pump assembly so no need to replace.

I'd definitely start with cleaning the throttle body and IAC and running the Seafoam. Then report back and let us know how it's doing.

 

Looks like it was a combination of things... When I went to check the plugs, one of the wires came apart (the metal casing stuck to the plug). Then when i pulled it off again the end of the wire completely separated... Replaced all wires.

I also installed autolite platinum plugs last year, and I did a little searching and didn't realize how many people had issues with them. Bought 6 new champion copper plugs and gapped them at .35

Sea foamed through vacuum and in gas tank.

Cleaned throttle body (was pretty filthy) and iac.

All seems to have done the trick! $35 and a few hours. Thanks again for the input