Well this is a two part post. Today I go out and start my 1999 Olds Alero GLS 3.8 and have a terrible rough idle. I put it in reverse to back it up out of the driveway and it felt like it was anchored to the drive. Now what would cause this to happen? I did a tuneup when I bought it roughly 15k miles ago. (new plugs, new wires, K&N air filter).

While I was at work a guy told me to take the gas cap off then retighten it. Well I did that tonight when I got home from class and it is running fine now. But what I don't understand is if my fuel system wasn't pressurized why would it take 100 miles (half a tank) to finally show up? I would still like to pull the code before I erase the code. Thanks.