[pguan]

P0171 P0174

2011 328i 73k miles

I have been fighting P0171 P0174 lean codes for months. I hope people can give me some insights. I have searched countless articles about this, and I hope I can pinpoint the issue given my unique symptoms.

Symptoms:
1. The car get these codes intermittently. I will get the code every 7 days or so assuming I drive every day.
2. These two codes ALWAYS appear together.
3. When SES light is on, if I stop the car, I can feel pretty rough idle. But before SES light is on, I really can’t feel anything wrong. It is not like there is a transition period that I can feel rough idles but no codes.
4. The car starts up fine every morning. There is no rough idle at the start.
5. [THIS IS VERY UNIQUE] The codes always come after I drive the car for 30-40 mins. My commute is about 10 miles with traffic. When it happens, the light is on towards the end of my commute.
6. When the light is on, I can always clear the codes with OBD tool and restart the car, then the car will be fine.

What I have done:
1. Inspect intake leak. First thing to check is intake leak since I always get both codes. I removed and reassembled the intake air box, boots, all the way up to manifold. On E90, the intake ducts are made by plastic, I did not see any where broken.
2. I cleaned and tested the fuel injectors. I made sure there is no clog.
3. I replaced valve cover and its gasket to make sure there is no air leaked into the engine block.

What I haven’t done:
1. I did not change O2 sensors
2. I did not change MAF sensor.
3. I did not change fuel filter (where is it on E90)

Any ideas? Thanks very much