171 and 101 come up as MAF and lean condition. On my wife's 2010 Mazda CX-7 2.3mzr turbo. 100k miles. Seems to run perfect. Stable idle and perfect drivability.
Through my phone I can see the raw data and they look ok. The maf is about 4g/sec and 19ish with light load. 50 at wot. Seems normal. It responds to throttle changes instantly.
the air fuel does look a little lean at 14.5 but I'm guessing new dfi cars run on the lean side. Air fuel changes instantly. The data looks the same cold and warm.
I cleaned the maf with rubbing alcohol even though it looked ok. No change, still got the same codes within 40 miles.
she does occasionally fill it with 87 octane, but I've never heard of that throwing a code
I have no idea what I should replace.
Look at LTFT (I think that's what the common name is). Probably over 25% off and tripping that code.
since it's lean, I'd bet there's a small leak somewhere.
oh, 14,5 is totally normal, since it's between 14.3 for E10 and 14.6 for E0.
Long term fuel trim and short term fuel trim added together will generally kick a 171 at 20%. Vacuum leaks, maf, o2 sensor, something in that range.
It's also possible to have ltft and stft argue if there is an intermittent failure.
Watch trims and drive the car. Light load high trims suggest vacuum leak, high load suggests sensors.
Look at idle fuel trims. (14.5 is slightly rich, not lean, but if the computer is in closed loop, it WILL be running at whatever the computer wants it to - that is the purpose of closed loop)
Also, clean the throttle body. I'm seeing more and more cars with drive by wire and turbos where they seem to be doing their idle fueling based heavily on throttle position. I assume this is because of the high volume between the MAF and throttle plate causing MAF sensor lag with throttle movement. Volvo was infamous for setting a P0101 due to a dirty throttle plate for this reason, but I havd seen some Chevys doing it too.
Dirty throttle body causes a correlation error between calculated and measured airflow, because the throttle plate has to be open further. The fault programming generally assumes that the MAF is bad.
Update. I cleaned the throttle body and now only get 101 for the maf.
the maf is super cheap so I just ordered one. I've gone through a whole can of carb cleaner and the idle is still perfect, so if there is a leak I can't find it.
