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Old 08-30-2019, 01:24 PM
Join Date: Aug 2019
Location: California
Posts: 4
Fandu is on a distinguished road
P0171 and P0174 on 2005 X3

I went through many posts regarding the 2 codes. 3 years back I replaced the boot and the car ran fine. Then last year I had white smoke coming from exhaust and ended up replacing the valve cover and gasket which fixed the smoke but then started getting the dreaded p0171 and p0174. Replaced the CCV and DISA as well.
Did a home made smoke test and no leak. Thought there might be an issue with my home made device so took it to an Indy for a professional smoke test. Nothing no leaks.

Trying to figure out what to attack next - spark plug, O2 sensor or MAF or anything else I may be missing.
The car has 136k miles and spark plugs were replaced at 86k miles (6.5 years ago).

Any help is appreciated.
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Old 09-01-2019, 09:45 PM
Join Date: Aug 2019
Location: California
Posts: 4
Ltomfohr is on a distinguished road
I've been having virtually the same problems with my X3 as well. I too have replaced the elbow boot, DISA valve, and entire CCV system and hoses.
In addition, I've also replaced gaskets for the valve cover, intake manifold, throttle body, oil filter housing, oil dispstick o-ring, O2 sensors, spark plugs, even coils, and a few other seemingly unrelated bits and bobs. Took it to an indy shop for diagnostic and smoke test and they couldn't find anything helpful... (granted they ended up being a pretty shitty place after several visits).

My case might be a different mess than yours, but so far I haven't been able to track down the cause of these damn codes, even after tons and tons of researching videos, forums, car-FAQs, etc. My fix doesn't seem to be what everyone else has had work. For a while too, one code actually went away and I was left with just the P0171.

Next up on my "To-Do" list will likely be checking and/or replacing the MAF, EGR valve and hose (since it's part of the secondary air system that plays a large part in the vehicle's emissions), and possible exhaust leaks that maybe I'm missing...

**One thing I did notice that I would've never thought to check was the fuses. Was rooting around the fuse box in the glove box for another issue, and realized that 2 of my fuses (of the 4) related to the engine control was missing! (Apparently this is something shady sellers can do in order to keep the check engine light from coming on or hiding things of that nature). Could be something as easy as that...going to buy some to test it out.

I've also read few bits of information here and there about possible clogged/dirty catalytic converters, leaking brake booster (less likely though), and even an issue with needing to update/reset/replace the vehicle's PCM/ECU (powertrain control module/engine control unit).

Not sure if that helps out much, but it may give you some direction if you're at a bit of a dead-end. Seems like I'm going down a rabbit hole with these codes, by this point the car's gonna be brand new! I have read that, oddly enough, O2 sensors are usually a last-resort replacement for these issues. So if you can, start with the cheap and easy fixes first and check off from there.
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Old 01-05-2020, 07:23 PM
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Join Date: Jan 2020
Location: GB
Posts: 209
getty150 is on a distinguished road
A good view...

Sent from my SM-J727T using Tapatalk
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Old 06-13-2020, 11:18 AM
Join Date: Jan 2011
Location: Houston, TX
Posts: 26
JP-X3 is on a distinguished road
Check the Oil Pan Gasket and exhaust vacuum flap lines

I replaced everything as well with no improvement. I then decided to replace the intake manifold gasket and found at the back of it there is a vacuum hose that connects to a canister used to "Store" vacuum for the exhaust flap valve. I decided to eliminate that system so the vacuum ports are now plugged and the X3 has a constant deep growl which is acceptable to me, a side effect, no more rattle.

Second suggestion: replace the Oil Pan gasket, sometimes there are small leaks that will suck air but only leak a small amount of oil (Right hand side, passenger side for USA). This is a major repair, took me 21 hours, I hate those power steering connections.

I did both repairs during the same week and voila, no more lean codes. Hard to pin point the culprit.

Good Luck!
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Old 01-11-2021, 12:57 AM
Join Date: Aug 2019
Location: California
Posts: 4
Fandu is on a distinguished road
Forgot to update:

Replaced O2 sensors but that didn't help.

Ended up getting a new MAF and it resolved my issues.
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Old 01-11-2021, 12:47 PM
Join Date: Nov 2018
Location: Canada
Posts: 634
c-bass is on a distinguished road
Originally Posted by Fandu View Post
Forgot to update:

Replaced O2 sensors but that didn't help.

Ended up getting a new MAF and it resolved my issues.
Thanks for the update
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