There are so many good documents out there for this swap, JEEPFORUM has some great ones, JP magazine, etc. A quick internet search yields good results. I find that even with every great writeup I have a lingering question, mainly due to lack or experience in the project itself. Please allow me to document this swap as I go and feel free to ask any questions or add suggestions along the way.
I started with finding my donor TB (Throttle Body.) I found it on an XJ with around 100,000 miles on it. I did not document the removal as I was in a pick n pull and didn't think of it. I always disconnect the battery when doing any work in the jeep as Im scared to death of frying the ECM so when doing this in your Jeep I recommend doing it, it will need to be done later anyway to reset the ECM so why not do it now and save the risk of damage. Next remove the large intake hose on the top running from the airbox and the smaller tube running to the top of the motor. Next you will have to remove the throttle cable and two plugs attached in the rear. A small flat head screw driver will facilitate this. Next remove the four bolts hold the TB on the manifold. Here is a picture of the TB removed looking into the manifold. (more on that later) Note the two plugs above and the cable below.
Now you have your donor TB you can inspect it for anything out of the normal cracks or chips in surfaces or severe burning should be avoided, don't worry about gunk and oil that is typical and will be cleaned later. Here are the side by side comparisons of the TB's. They are virtually identical with one obvious improvement from 2.5 to 4.0.
The 4.0L is the TB on the bottom of both pictures. Similar housings yet the overall interior area is Much larger in the 4.0L. It is possible to increase the size by machining out a little more from what I understand but I am just interested in a straight swap. Here is where most questions arise. You will need to swap the components from the 2.5L to the 4.0L in order for your idle to remain stable and to not create an engine light (CEL.) Yes folks they are TORX bits (star bits) and security torx bits (star bits with a raise nipple in the middle) just for good measure. So grab your set, if you dont have one by now go ahead and invest in a set, and a bag, can or handful of patience. As we all know you will need all of these for virtually any torx related removal.
The following is the same for both TB's.
I started with the IAC (Idle Air Control) valve. Remove it with the black electronic plug attached for the TB. You will disassemble it more later and clean it.
Here you can see both TB's one with the IAC removed and and the other attached. NOTE THERE IS A GASKET BETWEEN THE TB AND IAC ASSEMBLY. I broke the donor one so I was extra careful with the 2.5 one.
Here you will see some crud for sure but don't be discouraged its all a part of it. Now remove the other IAC from the other TB. Its not hard to confuse them as they are labeled but just in case you can mark them if you like. (I did as I tend to get ahead of myself.)
Now grab that patience I spoke of earlier. I had the same problem on both of the TB's when it can to removing the TPS (Throttle Position Sensor.) I think the torx screws are held in with loctite and no amount of PB Blaster made a difference. So in the end I used a small file and filed flat edges on the heads of the screws in order to grab it with a wrench. Hopefully your luck will be better but dont give up a small file will easily cut through the heads and this will not be the first time you will have to sit back and think about how you are going to get a Torx screw out.
So now you should have 2 TB's, 2 IAC's and 2 TPS's sitting in front of you. Go ahead and put the 2.5 TB, the 4.0L TPS and 4.0L TPS away. Now its time to clean what you have.
The TB will be full of crud and oil, using TB cleaner and a soft brush, go to town. Make sure to clean the opening where IAC attaches as it will be dirty and is important it is clean. See it below.
Gloves would be a good idea. I live in a condo where you are not allowed to work on your vehicle so I used a black plastic catch pan and just cleaned the inside of the TB getting what I could, I didn't clean the outside of the TB but it looks nice if you do.
Now we move to the IAC. Again we find Torx bits. Disassemble the two components carefully as there is an Oring in between the black plastic component and metal housing. Here is the assembly broken down, note the oring.
This is why the oring is important. It seals the housing to the IAC housing.
Here is the IAC cleaned up a little bit and then the housing as well.
Almost done. Just a quick pic of why we are re-using the 2.5L IAC housing. Note this little tab underneath, look at the 4.0L, yup its located differently.
The TPS needs no cleaning that I am aware of.
So now we need to start putting everything back together. I have never put a screw back into my Jeep unless it was coated in antiseize. So this is when I took a little time, cleaned the threads of all the screws and added a light coat of that magical goop. If anyone know as to why it would not be a good idea to use it in the is application please correct me. Go ahead and clean and inspect the orings you removed from both the IAC and TPS. Any cracks in either could result in loss of power and rough idle due to air leaks. So your end product should resemble this. But I'm sure yours will be much cleaner. Remember the end result should be 4.0L TB, 2.5L IAC and IAC housing and 2.5 TPS.
So at present I have a cleaned up and assembled TB ready to be put back on. Now earlier I mentioned that I would return to the manifold that I pictured. Turns out I have oil inside the manifold, the large air house from the air box and the a little oil in the airbox itself. After posting these pictures and having a discussion with fellow members, the consensus is that there is oil coming into my airbox from the CCV/PCV system (I have a 95.) I plan on cleaning all these components and then cleaning the top of the motor and cover to eliminate the oil problem. I will document this separately at a later date as unfortunately I have to take the Jeep out of my parking deck in order to do this as they are pretty strict about working on vehicles in our condo building. Be sure to inspect all of theses components and clean as needed. There are guys that leave this oil leak as it is not severe and doesn't bother them, so you decided what is best. Keep in mind what goes through the air tube dumps into the freshly cleaned TB so it makes sense to at least clean the tubes and airbox. Im going to go ahead an replace the filter as well.
Once I clean all these components this weekend I will document the cleaning and re-installation. More to come. Again any comments and suggestions are welcomed as well as corrections if I am doing this wrong. Thanks as always guys.