Long term fuel trims and p1174

[08SuperSierra]

Hay everyone 

so my 08 Sierra with a 5.3 has been throwing a CEL for fuel trim issues

1 code it will say bank 1 Lean 

and then another time it will read bank 1 system imbalance bank one 

so my long term fuel trims are around 20% both banks 

I have looked at the mV for the o2 sensors all read roughly 500-700 mv if you floor it the pre cat 02s will dip to around 40-100mv 

post cats stay roughly the same 

I’ve sprayed around the intake and injector area with carb cleaner and water, didn’t get any results leading to leaking gaskets 

maf was cleaned 

CEL started appearing when it was around freezing weather, and wouldn’t turn on until it cooled down and re warmed up 

I don’t know where to even start being I don’t believe it’s a underperforming o2 sensors 

as it could be a large air leak or a underperforming fuel pump causing a lean issue but it only throws a CEL for bank one?? But both banks at at 20%??? 

[davester]

Maybe check the exhaust manifold/exhaust pipe for missing bolts or leaking connections ahead of the O2 sensor?    With my LQ4, it's common for the manifold bolts to break off, and on my truck, a number did and the exhaust would draw air in, making the O2 sensors read lean.

[CamGTP]

Check fuel pressure at idle and under heavy load.