I have a problem with my '99 Explorer. It will start up but then surges up and down at idle and eventually stalls. Also, when driving it you must give it very little gas or it will braek down or miss but let off the gas and it idles again fine? I was told this may be O2 sensors? I pulled 2 codes " PO135" and " PO161" are these sensors located just after the manifold or and these the rears? Hope someone replies. THANKS
Since no one else is answering, I'll give it a stab. The way I understand it, Bank 1 is the passenger side and Bank 2 is the driver's side on a forward facing engine. The codes you got are for Bank 1 Sensor 1(P0135) and Bank 2 Sensor 2(P0161). The codes are " heater short or open" and " heater circuit fault". So Bank 1 Sensor 1 is the passenger side sensor before the cat and the other sensor would be driver's side after the cat. You didn't say which engine you have, 5.0 or 4.0. Sensor 1 on both sides is the sensor that gives information to the computer to control air fuel mixture by controlling the fuel injectors pulse width. Sensor 2 is after cat and is a catalyst monitor.
I would check the wiring going to the sensors. I've seen sensor wiring heated up to where it was brittle and fall apart when you touch it. It seems funny that both sensors, on opposite sides and one forward the other after cat would go bad at the same time. The sensors could be bad, but again, I would check the wiring very closely. Do this when the engine is cold.