Welp idk where to start here. I got a 1999 Jeep xj with the 4.0l Welp the other day I noticed it started idling weird and then it had like a lop and started to surge when in gear then in neutral it sounded like a cammed big block....
Ok well heres what I did Its just a trail jep but its annoying. Ok I removed the cat,New IAC,New TPS ,Plugs,Wires,Airfilter and it fixed it for a little then I would get a random missfire then i rev it and it would go away. Well now Today I went to get diesel for the heater for my shop and it died twice and ran like total crap. then it wouldnt rev past 3k and it sounded like it was off the revlimiter and only doing 30mph. Then I let off then floored it and it was fine for 500ft and did it agiain..... Im stumped... and the part that really pisses me off the OBDII plug wont read...... idk and the fuse is good...
Please help.....
Thanks
Ron

 

Also has 4.6 Mustang V8 injectors

 

It sounds like a CPS problem...

However, for good measure, I'd clean ALL grounds and battery connections, make sure battery is good and check for vacuum leaks (given your surging idle).
You already have a new IAC and TPS, plugs and wire: just add the rotor and distributor cap and finish the tune up that way.

But I would be leaning towards the CPS if this has not yet been replaced by a quality one; you can test it (do a search) to get an idea, however when mine went out, (including semi-fried wiring), it still tested 'ok'...

 

So, how are things going with this?

 

Well, more then happy to help, but following up on your own thread might be handy....