[videosmithlaguna]

Well I am on a hugh bug hunt. My 2001 Hyundai Santa Fe that I am giving my 16 year old son is throwing the code p0171 to lean bank 1. It has a major tuneup including PCV valve, I cleaned the Mass Flow, replaced the upflow sensor and had the exhaust manifold soldred by a radiator show because it had a small crack. So I was driving today and again it popped up-WTF. I am at my wits end, I guess the Mass Flow could be bad but I doubt it.-Thank You

 

[sbr711]

I will assume this is a 2.4L we are playing with...

You cannot solder a cast iron exhaust manifold.. if it's cracked, replace it.. the crack and associated air leak into the exhaust tract will goof the Ox sensor to no end.

Look and make sure the PCV hose is not collapsed/cracked wide open, very common occurance, the vacuum leak there will give you a lean code.

Spritz carb spray carefully along the seam where intake gasket is, not common for gasket leak, but anything possible.

Another source of lean would be insufficient fuel pressure, verify correct.