Help, I'm reading +28 % in long term fuel trim at idle.
I don't think this is normal.

What could cause this problem?

 

have you ever replaced upstream o2's? they are recommended replaced around 100k.

 

yes, i have replace two O2 upstream sensors and actually the waveform is oscillating between 0.1volt and 0.80 volts and the mass sensor signal voltage is good. So i don't know where to look know.
I have replaced one of the hoses from the brake booster to the intake in which had a pinhole.

 

If you go under search you can find where they explain the fuel trims. It will give you a bit more insight, and I think a better understanding of why your fuel trims read as they do.

https://www.f150online.com/forums/ch...long-term.html

 

You have two threads going on the same issue.
Get the 171/174 codes fixed and the LTFT will return to normal after a few drive cycles.
The 171/174 issue changes the short and long term trims until the correct A/F is detected by the OX sensors.

 

This problem was associated with a p0171 and p0174 lean bank one and two. I replaced the Isolators bolts and the gaskets under the plenum, it was a four hour job but it did work, No engine light ON.It seems hard to do this yourself but it's all just time consuming.if you can't seem to find a problem with vacuum lines or the egr then look to replace the isolator bolts and plenum gasket.