This is for my girlfriend's STOCK mustang. I do the basic maintenance on it but other than that dont poke around on it too much. This is for an 01 mustang 3.8L. It has 96,000 miles on it. About 2 weeks ago I got the p1285 code and was getting bad mpg's. Went to advance and it said fuel air mettering. I assumed this was a vaccum leak. Search the internet and it said it could be a cylinder head over temp. I dont think this is it b/c all the guages are normal and it doesn't run hot. So i check for vaccum leaks and replaced air filter (needed it). Came up with nothing. It runs fine except for at idle where it is rough. The rpms range from 800-1000 while idling in neutral. It goes down a little when in gear. I'm not sure if its idling to high or too low. So i was stuck. Last night i changed the oil in it and ran some seafoam through it. Half in the gas and half into the vaccum system. Before i was done putting it in the vaccum hose it started smoking inside the engine on the passenger side, near the upstream O2 sensor. By the time i got my light out and started looking it was about done smoking so i didnt have much time to look. After the seafoam went through the system and was gone, the smoke stopped. This makes me believe there is a leak somewhere, but not sure where it could be coming from. One of the O2 sensors was replaced a few years ago by the stealership. Sorry about the long post, but i figured the more info the better. Thanks in advance for the help. Also, last night i noticed there was water constantly dripping out of the tailpipe.