Yeah Alpac ... I've been searching to see if I can suggest something but you've already hit on most of the stuff in your post (MAF, O2 sensors, etc.) I was hoping somebody would post something by now too.

I was gonna suggest the gas cap thing but it doesn't seem to be related going by the error code.

You might just have to bite the bullet and let a shop/dealership diagnose it for you.

Good luck and keep us up to date on the resolution.