Hi Zack, I had the same codes on my '99 a couple of months ago, here are a couple of links with lots of info. I had the air change over valve replaced at my local indy porsche mech. under $300 No cel since then.
http://www.renntech.org/forums/lofiversion/index.php/t628.html
http://mike.focke.googlepages.com/checkenginelightcausedbymassairflowsensor
later
dave