I have a problem with my liberty that the mechanic cant figure out the car starts fine when its cold but when i run it for awhile and let it sit for 5 minutes the engine doesn't want to turn over .I got stranded the other day came back to it after a fiew hours and it started no problem, i took it to the mechanic and he said there was a misfire on the spark plugs he loooked at the plugs and they were fine it said cylinder 6 was misfiring, and also the o2 sensor by the manifold is bad but i dont think that is what it is because its been bad for 2 years, ive tried cleaning the throttle body, putting injector cleaner in it all doesnt appear to be working. Oh and also the jeep is 2005 limited 3.7 4x4 it has 170000 miles on it and im hoping to get more but if it strands me again at my job id have to get rid of it our get fired so someone please help