P0171 and P0174: intake gasket and MAF drift

P0171 is bank 1 lean, P0174 is bank 2. On the AJ-V6 they almost always arrive as a pair. Two faults cover most of them.

1. Valley gasket

The lower intake gasket shrinks and leaks un-metered air into the valley. Smoke-test the intake with the engine off. Renew the set, do not reuse the old bolts dry.

2. MAF drift

At hot idle a healthy V6 MAF reads in a tight grams-per-second window. High or noisy, clean it once; if the number does not return, renew it. A contaminated MAF will lean both banks without a single hiss.

Do not throw O2 sensors at this first. They are reporting the leak, not causing it.