I wonder what the difference between the air/fuel sensor and an O2 sensor is, since they seem to be doing the same thing.
On my O3 FSM, it just lists it as two oxygen sensors per bank. So the AF sensor is just an O2 sensor, which is not $500! The part is between $100-200 depending where you buy it from.
2003 Midnight Blue SE AWD w/VDC
Colgan Bra, Mobil One, JWT POP charger
PAC aux input adapter, hardwired Escort Passport x50, KUDA mount for MP3 player, Porterfield R4S brake pads (now Akebono ProACT), ATE Superblue
Yokohama Envigor (much improved over stock Goodyears)
Lots of squeaks and rattles.