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 ??

 

A code P0171 may mean that one or more of the following has happened:

The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters (K&N, etc.) can cause the MAF to become dirty if the filter is over-oiled
There could be a vacuum leak downstream of the MAF sensor.

I would guess a likely culprit to be a vacuum leak. This happens more often then not. A lean condition can also be caused by an intake leak, bad gasket. A way to check this would be to use an unlit propane torch and go around the intake, should the RPM's pick up at all you have an intake leak. Gaskets are notorious for leaking on this car.