Hi guys, this is my first post in these forums. Im having issues with my 1999 Mustang GT regarding idle and an o2 sensor. Starting with the idle, without ac on, the car will idle at 950 to 1k rpms. The moment ac is turned on, the idle immdiately goes down to 700 to 750 rpms. It can also start surging sometimes between 500 to 800 rpms while the ac is on and off rarely but at higher rpms. Sometimes it will stall. The problem with the o2 sensor is bank 2 sensor 1. On the scanner bank 1 sensor 1 reads normal voltage above 0.1v but b2s1 always reads low voltage usually around 0.02v to 0.04v. Im getting codes p0133 and p1151. I saw a small exhaust leak right before the problematic sensor and it was welded but the voltage remains low. The sensors were replaced a few months ago and still getting the codes and weird idle and running rich. Sometimes the long term fuel trims can be high above 15%, other times they are low near 0%Any suggestions?