I know you said you replaced the MAF, but have you tried unplugging it and seeing if it runs any better? It may idle bad at first and need some throttle to stay running but should eventually run on its own. Just take it for an EASY drive (NO BOOST) and see how it runs. It's possible that you may have a bad MAF, either that or it's dirty somehow.

What brand and type (copper, platinum, etc) of plugs did you use? Part # from them?