Hey y'all,

new to the forum, as well as Jeep life.

I picked up a relatively mint '98 XJ Sport last month, and I've been having issues with a rough idle/misfire. I have recently rebuild the exhaust, Put new brake lines on, and some other necessary upgrades. The issue I'm having with it now seems pretty common, I've explained it below.

1. It starts up great, runs for about 20-30 seconds then it misfires/rough idle

2. I hit the gas but nothing, then it "catches" and revs high and bucks forward, then drops again.

3. After doing this for 10 seconds it returns to normal and drives incredibly smooth for the rest of the time.

*if I'm waiting in traffic or slowing down it stalls*

I have replaced the plugs, the old ones were worn and it didn't seem to make a different, Im thinking that it may be an O2 sensor, or an issue with the throttle body? maybe MAP or TPS? my mechanic didn't seem to think so but I'm not too sure about him anyways. Im definitely not an experienced mechanic, but have done a reasonable amount of repairs on my old 4runner, so I'm just looking for some advice on what I can do next. The fuel pump is fine as well, I just had it checked out.

Thanks!