This code came up. (I have VWs too, and there I have a VAG COM software, so I can monitor long term, short term fuel trim and O2 sensor, so I can pinpoint the cause of the issue with that and some propane. I only have a AL329 scan tool for the other cars.)

How could I figure out where the problem is coming from? Leak, O2 sensor... ? I worked on the A/C of the car before the code came up. I don't think I knocked on any tube doing that (seems the evaporator leaks, if that makes any difference). The manifold tube looks ok. Spark plugs were replaced about 3 months ago, I don't feel any misfire. I cleared the code and my daughter said it came back after like 30 min of driving.

Thank you in advance.

 

For P0171, the issue can be due to a dirty mass air flow (MAF) sensor. Get some CRC MAF sensor cleaner to clean it and see if it resolves the issue. Also, check the air filter and the housing.

 

Many thanks. Will check this evening and report back tomorrow if the code reappeared.

 

Was driving to gym while monitored short and long term fuel trims. When parked, and idling, the short term was 40%+. Long was maybe 3%. Before leaving the gym, cleared codes (no code but reset STFT and LTFT to 0). Coming home I picked up a new air filter, was 1 year old, and at home I vacuumed out the Mass Air Sensor. Reset the FTs again. Then was driving 10 min, and both STFT and LTFT were low and also when idling, they were normal.
Seems the MAS was dirty, thank you for the advice!