My truck is throwing the codes p0171 and p0174. It's on a 1998 4.6 v8. I replaced the vaccum hose to the back of the intake manifold/to the pcv valve, cleaned and checked the current for the maf sensor, checked for leaks on the intake, and replaced the pcv valve. The codes went away for about 2 weeks and now it's back. What should I look at/ replace next?

 

Intake gasket. May be a minor leak that's giving you trouble.

 

Do I just need to buy a complete intake manifold gasket kit? If so, which one is one of the better ones? I saw there is a couple different brands

 

Yes. Either fel-pro or motorcraft

 

Okay thanks!

 

Both banks are positive for lean, -so look at the air intake. Make sure the MAF O-Ring still exists and that everything is tight, - no leaks. Like your IAT grommet. That can't leak either.

When troubleshooting, keep in mind that BOTH banks are positive for lean. This usually indicates a problem just before the plenum and manifold.

 

Ok I will look into that also. Thanks!

 

Another question....Do you have a cold air intake? Some of these do cause Lean codes over time, even with no hose or manifold leaks.

 

Yeah I do. I have the k&n 57 series cold air intake.

 

What do I need to do in order to fix that?