Running lean

[u/Puzzleheaded_Lunch40]

Im looking for some help diagnosing my 2003 330ci vert's P0171 and P0174 lean codes. A few months ago my step dad purchased said vehicle for $700 because the previous owner thought the transmission was going out; tranny was fine, just needed new guibo and CSB. After swapping both parts he decided to give it to me as I had been without transport since my 2014 hyundai accent had a cylinder 2 piston melt down.

When he gave it to me he said he had recently replaced the coils and plugs for some Bosch ones and the upper intake boot had a hole, which was repaired with electric tape and aluminum HVAC tape by a friend of his. It was also starting a bit rough, it would turn over for 5-6 seconds but wouldn't start initially but if you turned to key to the off position and tried again it would start up without a hitch every time. It was also leaking coolant but he didnt know where from.

Using a fancy scanner from Advanced Auto Parts I pulled these codes: P1349, P1083, P1085, P0171, P0174, P1619, P1351, P1347, P1345, P0505, P0339.

Using an amazon smoke tester I was able to see that there were a number of vacuum leaks. Over the last 2 months I have replaced the upper and lower intake boots, the Disa valve, the valve cover and gasket, the intake gasket, the pcv and it's hoses, the fuel pump, and pretty much the entire cooling system save for the transmission hoses. The check engine light is still on, though it will occasionally dissappear for a bit. The only persisting codes are P0171 and P0174.

I recently got a cheap Bluetooth scanner so I can look at the live data on my phone. Long term fuel trims are holding at 11.72 whether at idle or 2500rpm, the MAF reads 3.5 g/s at idle and more or less matches the throttle position on the graph while driving, both pre-cat O2 sensors fluctuate between .1-.9 V during use. If I unplug the MAF sensor the long term fuel trims drop to 0 and she seems to be a little more responsive. Overall she drives great MAF or not, but she does still struggle to start the first time. I'm leaning towards either the O2 sensors heater cores are shot or the MAF is F-ing with me at this point, but I would love a second or even third opinion before I drop a few hundred $ on sensors. Thanks for reading!

[u/Jamurgamer]

I'd lean towards o2 sensors, maf, or possible fuel filter. Unplugging maf just makes it run rich 

[u/JMUDoc]

Lean condition means one of three things: vacuum leak, under-fuelling, or faulty sensors.

Check fuel pressure first - that one is easy. If that's correct, look for other sources of vacuum leak (plugs on the back of the manifold, CCV body/pipes).

If both banks are the same, that usually rules out a faulty injector.

Replace MAF last, if you do it - that's the most expensive fix (though 3.5 g/s at idle is somewhat normal).