I have a 2002 Chevy Impala, Engine light came on again for code P0171. Had the oxygen sensors changed a while ago. I was wondering if it could be from air in the cooling system. I had like a brown sludge on the radiator cap and I flushed it about 5 months ago, only the radiator, not the block and now I see the sludge again. I didn't know how to bleed the radiator so could air in the cooling system be causing this problem and code ??

 

Emission fault code P0171 = system too lean ( bank 1 ) referring to the fuel system.

I doubt air in the cooling system would have anything to do with this.