[boostedG37]

I just got a 2012 328i with N20 engine, and previous owner said he couldn't register it because it had some codes so that's why he wanted to get rid of this car.

The only code it had was P0171: System too lean (Bank 1)
He was using regular 87 fuel, so I put premium 93 octane from a Top Tier brand and reset the code.

It didn't go away, So I started changing some parts, so far I put four new OEM NGK Spark Plugs, and have some coilpacks on the way.

I changed the piping that goes from turbo to intercooler and from intercooler to the throttle body with the KIES kit.

I changed the oil, I put Mobil1 5w30, I know I made a mistake here so I will put Castrol European 5w30 soon, but at least I changed the oil, and it had about 7 quarts, give or take. Probably someone did a mistake and put the amount of the xDrive 328i, but this one is RWD so I put 5 quarts.

I changed the PCV valve with a new Dorman brand, put a new Denso air filter and a new belt, just because I was there.

When I'm flooring it, it throws the error P0234: "Turbo Charger Overboost Condition" once it shifts, so maybe could it be the diverter valve?

I'm more worried in fixing the P0171 "System Too Lean" so I can pass smog test and get a plate for it.

I have a NEW OEM MAF sensor on the way. I'm 99% sure it has nothing to do but I'm running out of ideas. MAP and MAF looks clean, but I sprayed some CRC MAF cleaner anyways.

The car feels smooth, idles perfectly, doesn't run rough at all!
Idle fluctuations are up to 15RPM so it's really steady and feels good overall.

It has just 94,000 miles on the clock.

Once I clear the codes, I can drive it for one hour or more and no codes, but once I shut down the engine and turn in on again, the P0171 Lean code comes back, and the overboost code ONLY if I floor it for five seconds or more.

I have a bluetooth OBD scanner but I don't know what app or how to see fuel trims, I have a boosted G37 with Ecutek and that software is awesome for datalogging and examine fuel trims, but here I don't have an idea how to see my fuel trims to diagnose it better.

Any ideas or pointers? I'm kinda lost now, I'm about to change MAF and new Delphi coilpacks but I doubt that's the issue.

Thanks in advanced!

[addicted 2 turbo]

I have the same the issue with mine, 2012 N20 328 and I replaced the MAF, coils, And spark plugs. LTFT Fuel trim at idle 29.69 and will go down if i rev To 1500 RPM. Did a smoke test and couldn't not find any vacuum leaks.

[BennettBucsFan]

If you just bought the car and don't know the history it's possible that someone put the wrong type of injectors on it. I had to replace my engine and when I left the new injectors on which were EU6 I kept getting lean codes even after updating it in ISTA, once I put the old injectors on which were EU5 and updated the numbers in ISTA the lean code went away. It's a long shot but worth looking into. I never would have thought that was the issue in my case.

[boostedG37]

Update!

So I went to a BMW specialist in my area.
They had the car for SEVEN weeks! but today it's finally finished...

They told me that the engine was changed by previous owner, and whoever did it, didn't do a great job because the vacuum pump got damaged, a few vacuum hoses as well, and the high pressure fuel pump pigtail.

Also they found some epoxy fixed vacuum fittings, a bit clogged (no leaks, but obstructed) this made the diagnose a bit harder.

Fuel pressure sensor was damaged as well, that was causing the overboost error.

I changed the PCV valve, and they noticed that (I don't know how) and suggested to change the valve cover... Okay, whatever is needed to fix this...

I pointed out about the injectors being EU6 instead of EU5 and they say that they are the correct ones and they match what's on the car's computer.

The good is that it passed emissions so I'm going to be able to get a plate.
The bad is that they say that it's lean only at idle, but it works perfectly fine while driving (no lean condition anymore). They suggested to try with new injectors and programming, but didn't guarantee anything.

The error came back as they said it might happen, they told me to drive it a lot and see how it behaves, and after a few weeks/months, try new injectors if I want.

It's so weird, maybe the gasoline went bad after three months in the tank, I only filled once and the previous owner had it for two months and sold it because it was a big headache not being able to fix it and pass emissions; he told me he filled up with REGULAR 87 oct. then I filled it once, mixing that old 87 with new premium 93 oct.

So maybe it could be something with old gasoline mixed with older lower grade gasoline from previous owner... unlikely but for now I want to try that before throwing more money into it.

Any suggestions?

Edit: Good part is that the car looks like new, Zero rust, no accidents, clean overall; and now the mechanic told me that the new engine looks perfectly fine while they were changing the valve cover. So I'm looking forward to fix it and keep it. It's my first German car and for now my first impressions is that it's over complicated xD

[brokenbeemer]

I recently got a 2013 328 and swapped the engine. The engine runs good but I have the same P0171 code.

What exactly did the specialist do to fix the code?

I checked for leaks with smoke and found nothing.

I replaced the fuel pumps but the code still remains.

Should I just check the vacuum pump/hoses, and the high pressure pigtail?