Lean system codes

[elgineddie]

Hey team,

Been a while since I've been here but I always know where to come for the good stuff!

 

I have a 2001 K2500 'Burban with a 6.0L. It's been acting weird lately. When it's warmed up and I'm at idle in Park, the idle is erratic and every few seconds there's a bit of an rpm drop (like when you pull off a vacuum hose and put it back on really quick).

I hooked up my code reader and it's showing P0171 and P0174 which is left and right fuel banks running lean. I have no clue where to start on this. I checked everything I could visually. I pulled the EGR valve and it isn't sticking. I guess a plugged fuel filter MAY cause some errors if there isn't enough fuel to pull but, again, I haven't a clue. I did a search on those codes here on this forum and found someone posted that it could be intake manifold gaskets but I sure as heck don't even want to start thinking it's that!

 

I had the Hypertech programming in but I removed it, reset the codes and drove around until I got the same codes so it wasn't the programming. I do have a Granatelli MAS installed and I thought I remember someone once telling me those can throw a lean code.

 

Any other ideas on where I can look?

 

Thanks!