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I am working on a 2014 Nissan Altima with a P0101 MAF sensor range. No driveability issues.
I noticed that in the freeze frame data that code was set at idle with the engine warm.
I checked fuel trim and noticed a -10percent long term fuel trim at idle and +2 percent. As I increased RPM the fuel trim improved but was still negative at around 5 percent long positive 2 percent short.
I checked the air filter box and there was a big wad of some kind of lint in the inlet passage and the filter needed to be changed. I changed the filter and cleaned the inlet thinking I had the problem solved.
When I rescanned the car the idle fuel trim did not change. However the above idle went to -5 percent long trim and +4 percent short term which based on what I thought I knew I had done something by changing the air filter. I also noticed that the air flow rate from the MAF was slightly higher than before. which pointed me away from the MAF (maybe prematurely)
It bothered me that the idle fuel trim was still so negative but it was my brothers car and we were out of time so I told him to drive it and no surprise the code came back.
I checked the second time and there is a service bulletin on this car that says if it has an orange color PCV valve to replace it. If the PCV valve is black do not replace it. I am wondering if anyone has come across this problem before and what the difference is between the two PCV valves that would cause a P0101
The TSB also says that the computer may need to be reprogrammed. I just want to exhaust all options before I send him to Nissan to have to computer reprogrammed.
I suspect the engine is ignoring the MAF and running substituted default values. MAF sensors are very sensitive and are easily damaged also any change in the airflow pattern before or after the sensor throws the sensor calibration out. As suggested by Monde look at the MAF airflow numbers and also the data from MAP at key on engine off and at idle to see if the they are normal for your locations height above sea level.
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