Mass96XJS

My XJ has had a rough few days. It started with a bad idle while in drive/reverse and only when fully warmed up. It was accompanied by the temp gauge jumping up and hanging around the second to last line. It seemed to get better when the gauge came back down. With how old and dusty everything looks, i figured i would do a quick search and replace the sensors that had to do with idling. Ive replaced the throttle position sensor, the idle air control valve, the crank position sensor, and the forward O2 sensor.
After taking it for a test drive the gauge doesnt seem to jump up anymore, the cold idle is way better than before but its still struggling to stay going when idling in drive and reverse when hot. After it fully warms up, it starts knocking reeeeeally bad. I havent tracked too far in to the knocking but it sounds to be coming from the mid/front of the engine, which i think rules out the flex plate.
Power seems to drop off a bit when the knocking starts. Brought it to AutoZone and had it scanned. A code came up for the Transmission control unit and the torque converter. I didnt even know the tc could throw a code.

I dont know if the knocking and bad idle are connected but they started at around the same time. I should mention that the idle goes back to normal and the knocking stops shortly after going in to Park or Neutral.

The jeep is a 1998 4.0 XJ with US emissions (not CA)

Ive searched around the interwebs but havent come up with anything that i can find that would cause one or both of these that i havent replaced. Any direction from here would be a great help.

And yes, i made this account when i had a 96 xj in MA, lol

cruiser54

Check to see if your flexplate to torque converter bolts have loosened up. Link below:

https://www.cherokeeforum.com/f51/ho...ocking-125547/

Mass96XJS

The flexplate bolts sound like and they are definitely in need of tightening now that i hear the before and after in the link you posted.
But i'm wondering about the knocking that doesn't start until its warmed up and gets worse under load. I was hoping not to have to tear in to the engine to find out whats going on but white steam has started to come out where the head gasket is, so i guess i will find out the hard way.......
I cant get too upset, this is the first set of issues this thing has had in 4 years but damn it sucks

cruiser54

Just do the flexplate bolts and see what happens. It will take half an hour.