P0171 and P0174

After a few weeks of smooth running, I see the check engine light, I thought it was the fuel cap not tightened.  Fired-up Torque and the codes P0171 and P0174 came forth from the engine management system.

P0171/P0174 means the fuel/air mixture is too lean.  That means a) too much air b) not enough fuel c) some combination of a and b or d) a defective sensor.

Air?

In the case of d, we'd be looking at the mass air sensor, but let's assume our sensor's telling us the truth and we're not getting enough gas or too much air.  Let's start with the air: I checked under the hood and the path from the filter to the throttle looked OK.  That leaves the intake manifold seals.  Not sure how old those are, could be the culprit.  Alldatadiy recommends that I also check the EGR system as well, that seemed to be OK.

Gas?

Next the gas: No leaks.  The filter (sorry, no picture!) appears to be old -- could even be original.  The fuel pump might not be moving the fuel to the I'd start with replacing the fuel filter and see if that helps.  But first, I'll clear the code.  If the code appears again, I'll know it's not just a ghost in the machine.

Environment? 

It must might be the unseasonable temps and the huge dip in temperature the last few days.  Here's last week weather thanks to timeandate

Maybe there was some condensation where there shouldn't have been with the quick dip in temps.  Or couplings cooled at different rates, allowing for some leakage. If the code doesn't come back, I'd attribute it to the sudden shift in weather; but, I think that's wishful thinking and something will need to be fixed in the near future.