Mechanic Q: My 2006 Ford Focus has a rough idle and is randomly stalling?

I have a 2006 Ford Focus ZX4, SE, 2.0L. It idles rough with loud vibrations. More importantly though, it recently has been stalling as I slow down to stop at a light or make a turn. It turns back on, but it is just getting more frequent as time passes. The check engine light turned on finally and the code said P0171, bank 1 and lean. I replaced the oxygen sensor and it's still happening. I also replaced the MAF sensor and checked for any valve leaks and found nothing. Can someone please tell me what may be the problem with my car? I am out of ideas.

Q: What is wrong with my 2006 Ford Focus??

I have a 2006 Ford Focus ZX4, SE, 2.0L. It idles rough with loud vibrations. More importantly though, it recently has been stalling as I slow down to stop at a light or make a turn. It turns back on, but it is just getting more frequent as time passes. The check engine light turned on finally and the code said P0171, bank 1 and lean. I replaced the oxygen sensor and it's still happening. I also replaced the MAF sensor and checked for any valve leaks and found nothing. Can someone please tell me what may be the problem with my car? I am out of ideas.