P171 and P174 Codes
I have and 02 4.2L F150 that keeps giving me the P171 and P174 trouble codes. In other words, the left and right banks are running lean. The truck has 104K miles. Roughly 6 months ago the lower intake manifold was replaced (original cracked and I caught it early) with a used one for budget reasons 95k miles at the time. About a month later, the trouble codes popped up. I did move over to a cold air intake and have checked and sealed any possible leaks. I don't know how how to check the PCV valve because all of the repair manuals describe doing it on the V8's and I just get lost. At this point, my only guess besides the PCV valve is that the intake gaskets have gone bad. Any ideas?