I've got two or three codes that my monte is throwing. PO171 and PO172, Fuel trim system rich (bank 1), and Fuel trim system lean (bank 1). It throws one of each, or the lean code twice and rich code once. I talked to a mechanic friend and he thinks its my O2 sensors. Anyone else have this problem or ever heard of this happening? I also just switched back over to using E85 right after this issue came up. My mechanic friend said that E85 may bring up issues like this or might even solve this one. Anyone have problems using E85 or know other effects of using E85?

 

Try something other than e85 for about a week and see how tat goes.

 

The issue came up a few days ago and i first read the codes today. And tonight I started using E85....first time since last year when gas was high. So I the issue isn't the E85 right now. I'll see if it has any effect in the next few days though.

 

Ok, then it probably is your sensors. Or your pcm is going crazy.

 

or uve got a vacuum leak

 

most likely the sensor tho

 

vacuum leak....where? jw what all the possibilities are.

 

it would b on the bank one side of the intake manifold. u can check by starting the car and sprayin carb cleaner where the manifold meets the block and if the idle changes u know there is a leak. wd 40 works as well

 

Yep- sounds like a female pcm- it can't make up it's mind what it wants.

 

Your right! It is a female PCM...I pulled the battery today so I could see what codes come back. So now it's giving me the code that it's runnig lean twice and not rich at all. I don't get it.