My 97 Ford Explorer (SOHC - 4x4) has been idling horribly. It will stall out anytime you come to a stop. Sometimes, however, it seems to run okay. The Check MIL light has been on for awhile now. I hooked up a shiny new OBD II code reader today and I get 4 codes that all seem to point to an O2 sensor:

P0172 - Bank 1 too rich
P0171 - Bank 1 too lean
P1131 - Lack of HO2S11 - sensor lean
P0133 - O2 Sensor slow response - Bank 1 Sensor 1

This is my first time using a code reader. All signs seem to point to one faulty O2 sensor. My problem is, which one?? The Chilton guide indicates I have 4. Where is the bank 1 sensor 1? Left? Right? Nothing seems to pinpoint it in the book. Is there an easy way to figure it out without pulling all of them and testing the voltage?

Also, am I correct in my assumption as to it being a bad HO2 sensor? Any help is much appreciated. Thanks!

 

I've had simalar problems with my 2000. I would check out the IAC before changing any o2 sensors. Their is real good info on the IAC if you look on the main forum page at the first posts labeled "sticky". Check that out and keep us posted on the problem.

 

Thanks! That IAC post w/pics is extremely helpful. The resistance on the IAC seemed to be fine so I pulled that sucker off and cleaned the hell out of it. I'll see how it runs the next couple of days. I also bought the O2 sensor in case the problem remains. If cleaning the IAC did the trick, I can just return it!