Ok so I have been trying to fix my idling and lurching issue and I am now looking at the wiring. Keep in mind, the brand new rear o2 sensor is throwing a code, so I suspect faulty wiring. I cleaned a total of one ground lol. But, u found this ground here with no wire going to it (top right hand corner of pic) I couldn't find a random wire laying around so I was confused. I also found where these 2 wires are crimped together. Now these wires look like they could be coming from the o2 sensor, so could that be the ground wire for it? It's the black wire in the pic I'm talking about. Also, this is on a 99 xj and for reference this is in the back of the bay by the firewall, right in the middle.

I'm no wiz on your 99. That ground was added, not stock. Pretty sure those plugs are trany control/nss stuff. With the exception that if you have rear "post cat" 02 sensor it's (4?) wires may go through there. (a post cat doesn't affect running, just turns on the light)

I think like the earlier Jeeps, almost everything grounds there on, or near the dipstick tube mount. TCU, (your), PCM, injectors, all the sensors. All right there. You might look at Cruisers writing on grounds for our old Renix in the link in my signature. You may not have a separate TCU?, but allot may be similar.

Of course getting your codes read free at the auto parts, then posting the exact code might help. There are some here who are pretty good at that!

Of course your cap/rotor/wires are all clean and your (not platinum), plugs are gaped at .035. The gap gets a little bigger each mile, then eventually the idle will get rough. Idk about surging. You might look into cleaning the IAC. The Idle Air Control is a computer controlled "vacuum leak", not unlike the idle speed screw of old days. Guess they get sticky.

That is not a factory ground location. Most likely something some hack installed for lights, or something of that nature.

Those connections lead to the transmission (shift solenoids, TCC, VSS, etc.). Follow the wires from both O2 sensors to their connectors, pull them apart clean them and add some dielectric grease. Clear the code(s) and drive it for a while to see if they reappear and go from there.

Here's some images of the ground points in your '99 engine bay, and notations of what circuits are grounded at each point. Note that G102 (dipstick bracket stud should have two ground wires terminating there, both of which are the Data Link Connector grounds. The O2S ground at G101 is for both upstream and downstream O2S heaters. Your '99 ground points are much different than the RENIX Jeeps so be cautious of using any ground point guidance that originates from RENIX owners.

Thanks!

Great info and nice diagrams, as usual. Thanks Ken!

On a separate note. If I have it right Renix actually runs it's grounds through it's ECU to that dipstick stud. Presumably to protect the sensors from any "activity" from the ground side. Static, welding, lightning! reversed jumps....That's what I gather anyway.