Engine Won't Idle?

The day after I purchased this jeep it stalled as I was slowing down for a stop light. It started right back up and was ok other than idling a little rough at stops and some smoke coming out of the exhaust. On the way home from work that day the check engine light came on. The code said I needed to replace the upstream o2 sensor. I installed the new sensor, started it up and let it sit and idle for about 15 minutes.The check engine light was gone and it was great, no more smoke and the idle was very smooth, no more missing or erratic rpm's. Shut it off but restarted about an hour later to move it in the carport to replace the battery terminals that were trashed. I was having no problems with the battery but they were cracked and looked like they'd been beat with a hammer. I discovered that these were the terminals that had the cables attached which are not the kind I had purchased so I connected the terminals back up and decided to wait on them another day. When I started the vehicle it died immediately. That's what it's done every time since. I can keep it running if I keep my foot on the accelerator but its smoking again, a lot. When I do keep it running, most times the idle is erratic, jumping a few hundred rpm's then back down, and up again. There have been a few times that it's stayed running on it's own if I let my foot off the gas real slow but it hangs at 2 or 300 rpms and jumps up to 4 or 5 then back down like its going to die, then back up again. I put a load on the engine by turning on the ac but the idle doesnt move accordingly. As soon as I try to put it into gear, it dies. I spent days searching for a vacuum leak or loose connection somewhere to no avail. One odd thing I discovered is there are no relays in the PDC for either o2 sensor. Also, I found in the repair manual that when you replace a part relating to the exhaust system you need to have the codes cleared before you start the vehicle so I risked driving in to town to a shop but there were no codes to clear out. They cleaned the throttle housing and searched for a vacuum leak, still the same situation. Did I interrupt the process of the computer "relearning" the parameters by disconnecting the battery? Everything was great after the o2 sensor installation until I disconnected the battery. What could have gone wrong?? By the way, she ran fine when I drove her to town, very smooth, lots of power and only smoked when I first started out but again, I had to keep my foot on the gas when slowing down or stopping. Any help/suggestions would be appreciated!