Having BOTH banks lean PO171 and PO174 means intake or vacuum leak. Having an intake or vacuum leak and your car wont idle correctly.
Spray around your intake gaskets with the car running at idle does the engine stumbles if yes theres your leak, if no then it is a vacuum leak, very hard to find so my best advice is buy hose for .99 foot at Autozone and replace the lines till the idle stays normal and the code goes away.
