I've read the 2009 orum discussions on this subject. Didn't find their final solution.

My Check Engine Light ON. AutoZone scan tool showed error codes P171 and P174, which they said indicated was a bad MAF. I replaced it with no change. The Idle problem seems to have started here, but not sure because I don't remember having any stalls before. My scan tool also shows the P171 and P173 codes and a 300 stored code. At CL it indicates Bank 1 and Bank 2 SHRT FT @ +50. LongT FT @ +25. Both O2 sensors reading 0.045 and 0.035 respectively. MAF @ 2.06. Idle moves between 600 and 400. Sometimes stalls in drive gear. At 2500 rpm, the numbers come down, but always very high.

I made a smoke machine and smoke tested the engine three times trying to find a vacuum leak. None found. I replaced the fuel filter. Fuel pump was recently replaced. I checked and cleaned the EGR.

I'm lost as to where to go from here. Any suggestions?

 

P0171/P0173/P0174 means that the PCM is compensating for a perceived excessively lean condition. The MAF sensor may or may not be involved. Those codes are confirmed with your extremely high positive fuel trims. You add LTFT and STFT together and you have a positive value of 75 which may be the record so something is definitely wrong. That total is good below 10, and sets a code above 25. The system takes sensor input and produces the amount of fuel delivery (by varying injector pulse width) that the PCM lookup table indicates. After the engine warms up it goes into closed loop operation which starts motoring the oxygen sensor readings and adjusts fuel delivery to keep the mixture ideal for minimal emissions. The resulting departure from the look up table values is fuel trim.

Your lean condition can be caused by:

Sensor failure such as a bad O2 sensor, MAF sensor

fuel delivery is not as commanded to the injectors such as clogged injectors or low fuel pressure

Air leak after the MAF sensor (unmetered) from say vacuum, intake gasket, air horn after MAF, evap system

PCM failure

exhaust leak

Wiring or connectors


what else have you changed leading up to or after this problem besides the fuel pump and the MAF sensor?

Did you verify fuel pressure per the sticky after the pump change?

Are the individual bank fuel trims different?

What is your fuel mileage?

How is power under acceleration?

how much do fuel trims improve at 2500 rpm?

How many miles are on the O2 sensors?

Have you looked at the O2 sensor function on live data?


George

 

I had the exact same codes with the same fuel trim numbers. I exchanged my MAF sensor for a "known good" one, but it still didn't make any difference. It still fell flat on its face as soon as it warmed up. I ended up replacing the MAF again with a brand new Delphi unit (new style plastic one) and it's been running great ever since.

Just as a diagnostic tool, try driving with the MAF disconnected. When you do that, the ECM will substitute generic information and it should run better if your MAF is bad.