I am trying to figure out WTF is up with my car. After my first tune with a lot of timing, I was ripping it up one night, and after it I heard a big miss at idle. Never happened before that. Right before I heard the miss I threw a code for "system too rich on bank1 and 2". The next day I replaced the plugs, and I can still hear the miss at idle, just not as much, and normally after Ive been driving it for a while, and its not throwing any codes. I have since had it tuned by a different place and the tune is now better and tuned for the maf so I am getting no codes, just what sounds like a miss at idle. My question is, could a bad 02 sensor be my problem? I have been chasing this small problem for months to no avail. Thanks for any help.