I have an 04 fx4 5.4L. I have had a p0171, running lean bank 1 code on, and for a while it was intermittent, on for a hundred or so miles then would go away for a couple hundred miles. I was driving home with 3 other people and a full load of stuff in the bed and when I would accelerate uphills the truck would hesitate, then accelerate, but the cel would flash. When i got out of the high rpm's, my truck would kind of shudder and a vibration was felt throughout the truck. I figured it could be a bad ignition coil, so I put in new ones. I also looked for vacuum leaks and found none.
Cleaned the t.b. and maf, new fuel filter, new intake manifold gaskets, and I still have the code. When I am driving, besides hard acceleration, the truck drives fine. When I get to a stop sign or light, the car idles erratically, between 500 and 650, maybe dropping a little bit as well. It feels like it is going to stall, but never does. I only get p0171, and it sounds a lot like a diesel. I don't want to take it in, because it seems like the mechanics I take it to don't want to deal with the 5.4, but if there are any other checks anyone could think of that would be great. Thanks in advance!

 

Did you ever get your P0171 code, rough running thing figured out? I have the same issue.

 

I'm very interested to hear of the amazingly easy and free repair.


That won't be it on my truck, naturally, so I'm also interested in the expensive and nearly impossible to DIY fix.