2003 Ford Focus cutting out when idles

I have posted this problem before. It had a dtc 302 and 2274, well I exchanged coils 2 and 3 and reset the computer, and now it does't show any misfire, just the 2274 bank 1 02 sensor 3 is stuck on lean, it does't stall it just cuts out at idle only. So I was thing stuck egr it does't act like a vacuum leak, but I don't know how these new cars act with a vacuum leak, I know older vehicles when they had a vacuum leak you sometimes could hear the whistling or you could tell buy the way the motor was loping, that is why I say it does't act like a vacuum leak. Does anybody have any theory on this. And does anybody know how many volts a coil on plug should put out?