o2 sensor problem...

Well I've been having idling issues lately and and ocassional CE light pop on then off so I decided to scan for codes. Got one code:

172: Heated Exhaust Gas Oxygen (HEGO) sensor - voltage signal indicates "lean" (Bank #1).

First question: which side is Bank #1? Driver's side or passenger's side?

Second question: there's all sorts of other problems that could happen to o2 sensors like rich or not switching. How does "lean" happen? I just replaced these like 10,000 miles ago. I don't mind buying another one but I just want to rule out other things that could cause a "lean" condition.

Could my BBK longtubes have anything to do with it? They are ceramic coated and I've adjusted the Exhaust Pulse Delay settings like many of you have either done or recommended.

Thanks guys.

Hey Joe, I haven't been on here in like a month; I took a 12 day trip to Israel over the Christmas, so obviously Mustangs weren't the first thing on my mind. What's new with everybody on here? I bet atleast 5 people on here got s-trims for Christmas, lol. I gave myself a broken tranny for Christmas, hahaha.

Anyhow, turning up the FP is out of the question. For one, I already tried that and two it makes my car run worse. The car won't idle because the A/F mixture is somewhere in the 13.0's-13.5:1's. That's just with 2 psi. My car is tuned perfectly at idle (but not w/ a bad o2 sensor). Everything was fine, then just all of a sudden a lean o2. A/F with FP at 39psi fluctuates between 14.0 and 15.0. It used to be dead on at 14.7:1.

But which is Bank #2?