Rough Idle and P0136
 

Hello,

My 2003 expedition 4.6L is having issues. It has a varying idle (goes from 700 up to around 900 and back and forth). It is also throwing the code P0136. We replaced all 4 o2 sensors and the light is still on. (not worried about it since the car has 110k miles, we considered it part of maintence).

It kind of smells like it's running rich and that's what my buddy also thinks.

The PCV valve was replaced about 15k miles ago as well as the fuel filter. I checked the filter and it's flowing fine.

I don't really hear a vacuum leak from the PCV valve but it seems like that's a common problem. Should I take the hose off and check it manually?

I'm going to check the O2 sensor wiring to make sure it's not shorting out or anything.

Any other possibilities?

Thanks

The code PO136 suggests a sensor circuit malfunction bank1 sensor 2.
I believe you are on the right track in checking the wiring to the rear o2 sensor from the left bank at the converter. It could be something like no heater voltage to the sensor.
You might check all the fuses , one of them may supply voltage to the sensor in question.

The plastic boot on the pcv valve often caves in and causes a vac leak.

does anyone know which fuse this would be and where its located