I just got back from a trip to California. I own a 2009 Chevy cobalt 2.2 ecotec. When we arrived at a place to eat, my check engine light came on. It had a rough idle but ran fine. I made it home the same day fine and all. So I woke up today and I changed the spark plugs and the light is still on. I read a post a few minutes ago about how it may be the gas cap? Or maybe poor quality gas? I usually fill up at Smith's gas station (for those who live in Las Vegas or Utah) but when in California, I fill up with chevron. I haven't gotten to codes scanned yet because I was assuming it's just maybe the spark plugs. Can anyone who's had the same problem help me out? I'm about to go to work and I'll stop by and get the codes scanned after I'm off and let you guys know. Thank you!