Lions8150

Hey guys i just bought my first zj. 1996 laredo 4.0L quadra-tech loaded with all the options and 100k. I have owned and built a 1996 xj 4.0L. I am having a few problems that i was hoping to get some help with. First is the oil gauge, When i have been driving around for a little while it starts to act funny. When i break, the gauge goes from about 40 to 0 and the check gauges light comes on. When i start to accelerate it goes back up to 40 and stays until i break. The next is the check engine light. I took it to autozone and had it checked. There is two codes. On is the o2 sensor, easy fix. The other says ignition problem or misfire. Does anyone know what it means? They cant tell me. It has a new tune up so i dont think its a cylinder misfire. And the last problem is once i have been driving for awhile the screen by the shifter starts saying coolant temp sensor service. Is it really bad, because it doesn't draw a code on the check engine. And just tonight it started sputtering going down the street, almost like it wasn't getting gas, got off it for a minute and it was fine again. Any help would be great. Thanks.