My yj has been giving me some issues. She starts up fine and idles but as soon as I drive and stop like at my apartment gate or a light she idles speratically like 1000rpm to 500, back to 1000 then down to 500, and back and forth again. Kind of like loping or acting like its going to die then gets a jolt of energy . During acceleration she seems fine a little sluggish but that I think is due to me crappy welding my exhaust on "there's some holes in the pipe and makes the jeep sound like a rice burner since the muffler sits half way under the jeep. I have also been getting an lean code and an o2 sensor code. I was told by the shop that I had a crack in my exhaust manifold, and I know there's holes in the pipe as I can feel the hot exhaust air "popping" out of the exhaust hole. Does anyone know what might be causing it to idle like that? And for some reason my oil pressure sensor starts off regular and as the jeep heats up it drops to the second to last line on the gauge, is this normal? She seems to have enough oil. Any help is appreciated!