I hope someone can help, I bought a 2008 Jeep Liberty a month ago from a dealership. Since the day I drove it off the lot it has been running rough at idle. The CEL has been coming on intermittently with a P300 code. The dealership has change an O2 sensor, and plugs. Every time I bring it back they tell me that they don't see anything wrong with it. I'm not sure if it's relevant, but it rained really hard the other night and it's been running even worse since then. Has anyone had any similar experiences like this. Its a 3.7 automatic, with 42,000 miles on it. When I purchased it, it had 39,900. Any advice would be greatly appreciated.