2000 f150 4.2, pulls codes p0171 and p0174 (lean on both banks). Have installed new MAF sensor, replaced intake gaskets. Seems to run ok except idles 'bout 980 RPM. Have checked for vacuum leaks (starting fluid, carb cleaner and water. I will clear codes and they will be back 2-5 miles. Any and all help welcome

 

If there is no vacuum leaks you could try and pinch off the PCV line to see if that brings the idle down. PCV might be stuck wide open, (but I would think you would also get a code for over speed condition).

 

171 - 174 are almost always vacuum leaks. Easiest thing to check is all the small rubber hoses from the manifold to EVERYTHING. Truck is 16 years old... rubber gets hard / cracked / brittle ... small leaks. Pull one hose off at a time and check for flexibility and cracks.

 

2000 f 150 4.2 v6 232,000 miles

 

every thing rubber or plastic that you sprayed with carb cleaner needs replaced. That stuff eats plastic and rubber.