Having an ongoing issue with some mild performance issues and now recently fuel economy that has dropped from between 26-28 mpg to around 22. This has been consistently lower for a month or so. The code P0171 shows up intermittently.

I have verified fuel pressure at 30+psi at idle with 40+ psi with regulator vac disconnected.

My Egr valve is new and receiving vacuum, although it seems kind of low, I guess... 4 inHg at max. P0171 would indicate EGR valve open, where a low pressure would do the reverse, so not really worried about that.

My valves were adjusted about 20K miles ago.

I tried to check for vacuum leaks and found none.

I am down to looking into the primary O2 sensor and and exhaust manifold leaks.

If anyone has other suggestions, I could use a few good ideas.

Also, it seems kind of counterintuitive that I could have a lean condition while I am having poor fuel economy.

Thanks !!!

 

It most likely is the primary oxygen sensor. I recommend a Denso O2 sensor.