ok, so my car started throwing a code 13 on me. my mechanic said that since the air is getting colder, it's more dense and that it should go away on it's own. then, the same day he said this the car starts giving me code 13 and 1. oxygen sensor, right? ok, no other problems other than the engine light is on. so, i figure i'll fix it this weekend. then 2 days ago, i was giving my friend a ride to the airport and when i start it, it stutters. then as i start driving, at a stop it would stutter and stall. but it did start, and runs fine when actually moving. but as soon as i got to a stop, stutter... stop. i was driving it like that and then yesterday i was at a drive thru and got frustrated with the accelerting to keep it on, so i turned it off. after a couple minutes waiting, i started the car and the engine light did not come on. at stops it doesn't stutter or stop anymore. is this a gremlin that has come and gone, or should i change the O2 out anyway? thanx fo the help in advance.