Now that I look at your code again, you said "bank one" not cylinder one. Sorry, I read it wrong.... though I'm surprised no one caught me on that.
Actually, looking at it again you called it cylinder one in a later post. that is incorrect.
Engine use each manifold as a bank. Since this 4 cylinder only has one manifold, there's only one bank. So, that means your whole engine is lean, not a single cylinder. It may very well be the IAC, though I'm surprised you haven't seen another code for the IAC position.
Make sure that gasket surface is clean. spotless. You probably tore up the old gasket and just reinstalled it. That's probably why it runs like crap now. Since you'll have to take it off now, its up to you to test or replace it.
Keep in mind this still doesn't change the fact that your intake manifold gasket(s) could be bad.