i have a 2004 rx8 grey grand touring and just hit 60k and my check engine light came on and i check the gas cap and wont turn off. any advice before i go into get it checked out and waste money on something i can do myself? and ive also noticed here in portland oregon that the weather is colder now and while the car is on the car is a little shaky

only had the car for about 5 months bought at 57k
and also just got my oil changed like 2 days before the light came on

 

have the code read for free at auto zone, then post results here.