OBDII codes, PO135 & PO141 in 99 XJ

After coming back from a 650km trek and just installing a new water pump, the CEL came on and I have experienced some engine RPM issues. At first, the XJ had some hesitation in 3rd gear, then in second. Now at a stop light, the RPM's go to about 500, the vehcile feels likes it's gonna stall and the the RPM's shoot up to around 1500 and then go back to normal, then it dumps again to 500 and this cycle goes on. I can also hear the intake sucking in air as the RPM's are dropping.

I have searched around trying to find exactly what these codes could be and I am wondering if it is the same issue. I have used my friends OBDII code reader to find out what the codes are and here is what they were and the explainations according to "http://www.geocities.com/JeepI6Power/obd2.html" Here they are:

The PO135 code means "Upstream HEGO sensor response slower than minimum required switching frequency/Heating Element Failure"

The PO141 code means "Downstream/Pre-catalyst HEGO sensor heating element failure"

The generic codes indicate that the PO135 is a O2 sensor heater malufuntion bank 1 sensor 1 and the PO141 is an O2 heater malfunction bank 1 sensor 2.

Before I go out and buy 2 O2 sensors, does anyone know if it's common to have 2 O2 sensors go around the same time or if one sensor might be causing both codes?

Replace the front one first and see if that fixes it.

Thanks for the reply. I think that is my plan attack, we shall see in a few hours if that is the culprit.

Ok, so I've changed both O2 sensors and the engine is still running lean. The RPM's drop and then go up when it's about to stall. When the RPM's drop, I can hear the air filter swallow in more air. Any other suggestions?

still reporting codes at all? have you reset the computer by taking off the battery?

I didn't disconnect the battery, the codes were reset my a guy
@ Auto Value with an OBII sensor. I was told that disconnecting the battery did the same thing. 2 days later, it's still running lean and wants to stall out, I'm going through gas like a mofo.

Be sure to check the O2 fuses under the hood in
the Power Distribution Center(black box on passenger fender)
Eddie

Thanks, I did that. I think my exahaust manifold is cracked, well, I know. It is pretty rusty and I chipped at it to find a crack under the scaling. *bang's head*