So I've had this issue for a while apparently, thought I should double check with you guys before i go spending money on parts. When I replaced my intake manifold and fixed all my exhaust issues, I noticed my O2 sensor was unplugged. So I plugged it back in, and it drove fine for a couple days, although it wasn't driven much in those two days. Then it started running bad, started off it would idle fine but start skipping when load was put on the engine. Then it turned into skipping and running horrible from the time I cranked it up, and wouldn't stay running unless I kept my foot on the gas. Then it just wouldn't run at all. The whole time it was doing all this, it had good spark and good fuel pressure. So, out of frustration from not knowing what the problem was, I decided to try unplugging the O2 sensor, because the problems didn't start until after it was plugged in. And to my surprise it has run perfect since then. Its got me a little confused, because the only other time I had an O2 sensor go bad on me, it didn't suddenly run perfect after unplugging it. So is this my problem, or have I got another problem somewhere? I think someone told me a clogged cat could do the same thing, but it doesn't seem like it has a clogged cat to me, or at least it doesn't act like any clogged cat I've ever had before. But if it is the cat, now would be a good time to change it before I weld another muffler to the current cat.
So...what are your thoughts on this?

 

Renix O2 sensors work differently than most all others.

Is the wire harness burned anywhere? You mention it running real poorly and will die off without your foot on the gas?

I'm betting you have another issue to boot. The hose/pipe from the throttle body to MAP sensor may be cracked, split, melted etc.

 

I didn't notice any burned/melted places on the wire harness, but I'll check again, I didn't really look over that very well.
I did replace all the hoses and vacuum lines on the throttle body and intake manifold that needed it when I swapped intake manifolds. I'll double check it again to make sure I didn't overlook anything though.

Thanks for the tips Cruiser

 

You know, you had a bunch of stuff disconnected to do the work you did. Perhaps you should do my connector refreshing and inspect for any retracted pins in the connectors.

Also, the sensor ground test comes to mind as a possible area of problems for the same reason. You touched it.

I suggest unplugging EVERY electrical connection in the engine bay you can find, whether engine related or not, and spraying it out with a good electronics cleaner, visually inspecting the terminals making sure they haven’t retracted into the plastic holder, and then plugging it back together. There’s a critical 10-pin connector for the front lighting system located in front of the air cleaner and behind the left headlight assembly. Don’t miss that one. Also be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.
ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then plug them back in. I do this on every Renix Jeep I purchase or work on for someone else.
Revised 07/23/2012

Cruiser’s Renix Sensor Ground Test
　
This sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate.
Set your meter to measure Ohms. Be sure the key is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.
You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well.
Revised 06/12/2012

 

I actually did the connector refresh according to your instructions when I was putting it all back together. Second time I've done that on this Jeep (did it the first time when I bought the Jeep, after finding your instructions on it). All the connectors are clean and in good shape.

I have not done the sensor ground test yet though, I will do that as soon as I finish up my exhaust, and I'll double check everything else, all the hoses and vacuum lines, things like that.

Thanks again Cruiser, I'll post what I find in a little while.

 

Inquiring minds want to know......