Get some professional help. Find a mechanic familiar with Renix XJs and has the test set. Take it to him, pay for 1 hour of time and he should find your problem - one hour of labor is cheaper than some of the parts you listed.
You may need a throttle body cleaning is all but take it to a fresh set of eyes. How I found the tech who works on my 88 XJ was I called the dealer with a cruise control problem. I asked if they had anyone who was there when my 88 XJ was new. They then put him on the phone for me, I told him the problem and he explained what it should be.
I will say it was more than the things he listed but 2 months later he had it fixed and it only cost me 6 hours of time - book time for those new parts he installed. Every time I have had a head banger problem, I take it to Jim and while I am waiting he figures out the problem and fixes it.
I am lucky the tech likes older XJs and told me he'd like an 88 XJ to fix up. I asked why not a later one, he told me the only thing better on the later XJs is the electrical wiring, everything else had been "value engineered" away.
With the work you have done you may have a miscalibrate TPS. I installed mine using the volt meter method and the next time I had it into the shop Jim told me " I adjusted your TPS for you it was out of calibration." I now own the snap on MT2500 and my cousin's 85 vette had a non-smooth idle. After we went out driving we decided to set the TPS using the test set and the idle improved instantly. We then went back out and my cousin said he had more power. You may have the TPS adjusted too low, even though you used the multimete method. Since the TPS is adjusted wrong the engine never getting the right about of fuel for the amout of throttle you have given.
Thing off the top of my head are:
* Vacuum leaks - replace the CCV system tubes, also replace harness for front axle shift motor
* Dirty throttle body, they get that way if you have a bad EGR or you have the famous oil on the air filter problem.
* Map sensor is worn out, it can not adjust to the throttle response quick enough, solved by installing a new MAP sensor.
* Could have a CPS which is getting marginal, good idea to replace after 100K miles, also buy the high alt - gives you more advance and costs the same. No worry about ping since there is a knock sensor.
All of those fixes are close to what you will pay for professional help, go find a guy and have him examine it. Also ask if you can watch so you can answer questions for the tech. You know the tech never knows "all" the history you have done.
So call you local dealer, find that mechanic who likes 4.0 engines with the renix control system and you will have you problem solved.
