BMW 128i Fuel-Air mixture too lean

[trentonsandler]

For a couple months now my car (2010 128i) has been giving a service engine soon light and I’ve just gotten around to checking what it is with a bluetooth OBD II scanner. Its throwing codes P0171 and P0174 (fuel-air mixture too lean). To try to figure out what it is I’ve done a couple tests.

First, I checked the fuel pressure at the rail which is just above 70psi where it should be.
I also used to my scanner to check if the MAF was faulty, it isn’t.
Next, i checked the Short Term Fuel Trim (STFT) at idle and at higher RPMs to rule out a leak somewhere in the airways, and it was between -5% and 5% at idle and up to 30% at higher RPMs, which as far as I know ruled that out as well.

For some background on my car, last year I upgraded to the 3 stage manifold and put in an aftermarket intake as well as flashing it to the bimmergeeks 330i tune, so that shouldn’t be the issue…right? I did that over a year ago and the code just came up a few months ago

Any ideas on what it could be and what I can do to test it? I’m sure the STFT should not be getting that high at higher RPMS…

[4JawChuck]

Air leak somewhere, have you sprayed any connections to find the leak?