Ok.. After a thorough search, I have yet to find an answer.

I have an 09 MCS with 125k. I replaced the thermostat housing around 500 miles ago. I parked the car for four days this week and when I tried to start it tonight, it just cranked. I tried again and it started. It was rough for about 5 seconds, then settled and ran normal. I could smell gas and the CEL came on. It's throwing code 031 (increased emissions). I turned the car off and the fan kept running for about 5 minutes. I tried disconnecting the battery to reset the computer, and that seemed to work. Car started and the CEL was gone. I turned the car off, and again the fan kept running. Tried to start again... Crank, no start. Tried starting again, same stumbly start and settled back down and ran fine again. CEL on again as well along with the gas smell.

I've read that this could this be as simple as a gas cap or DTML. I also read on another forum this could be a bad temp sensor. As I stated before, the t-stat housing is new, along with the sensor.. I really can't afford the stealership, and would prefer to fix this myself if possible. Any suggestions??? Help!!