Hi Fellow Ford Enthusiasts,

I'm fighting this issue with my 2003 F150 5.4L auto. It runs okay cold but when warmed up it surges and hesitates and idles really low like it is in gear, even when in park. It was throwing P0171 and P0174 which is an oxygen sensor in bank 1 reading lean. I replaced the PCV valve setup it ran worse and then it threw P0307 which was a misfire on #7. I cleaned the MAF and changed the coil and it ran fine for about 5 miles when it started running like again, no codes showing at this time.

From what I've seen the culprits for code P0171 and P0174 could be;

MAF (this was replaced, not the issue)
PCV Valve and lines (this was replaced)
Air Filter (brand new)
Vacuum hoses (these were all inspected and/or replaced)
Intake Manifold leak (sprayed starter fluid all around and got no idle change)
Fuel filter clogged (was replaced less than 5k miles ago)
Fuel Pump (still original)
Fuel Injectors (still original)
EGR Valve (original)

So I'm pretty much down to the fuel delivery system as the culprit. I hear that AutoZone will lend out fuel pressure check tools so I am going to check there. Any other ideas?

 

Check the compression on all of your cylinders....