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The 2007 e92 325i with the n52b25 engine is experiencing a P0174 error code, indicating a problem with the fuel mixture. However, there is no evidence of a vacuum leak.

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Greetings, members of the forum,

I have lately obtained a 2007 325i e92. The check engine light illuminated with the diagnostic trouble code P0174, then faded and reappeared, consistently indicating the same code.
I brought it to a BMW expert who used an Autologic reader to get the codes. The diagnostic scan revealed two codes: 29E0 for mixture control and 29E1 for mixture control 2.
I requested him to do a smoke test, which he successfully carried out, revealing the absence of any hoover leaks. I requested him to inspect the MAF, and he informed me that it seemed to have been recently changed. However, he expressed concern that it may be a low-quality replacement purchased from Ebay. He is now uncertain about the nature of the problem.

The questions I have are as follows:

    What are the recommended subsequent actions for replacing the 02 sensor?
    Could the inexpensive MAF replacement performed by the prior owner be a potential cause of the problem?
    Have you examined the gasoline filter, pump, and injectors? (There was a substantial amount of dirt present around the fuel cap) I am wondering why I am receiving just one lean bank code when my technician is detecting both of them?

Thank you for your time and guidance. 🙂

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Disconnect the Mass Airflow Sensor (MAF) from your automobile and let it run for a few minutes without causing any damage. Afterward, proceed to check the error codes. Check whether the same code appears.

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Thank you for your response.
Will disconnecting the MAF sensor result in the generation of further error codes, since the vehicle will be unable to measure the air intake?
If the code does not display, it might be inferred that the sensor is defective. Is it advisable to reset the error codes before driving or should I retain the data and just let the vehicle idle?

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Update - the P0174 error code persists even after driving with the Mass Air Flow (MAF) sensor disconnected.

Does anybody have any insight on what will happen next? Is the issue caused by a defective injector or a clogged fuel filter?
Can checking gasoline pressure determine if the fuel filter is obstructed or not?

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The next aspect I would examine is the integrity of the oil filler car seal and the CCV (Crankcase Ventilation) system.

The ccv exam is rather straightforward. During idle, carefully remove the oil filler cap and place your palm over the hole (while wearing a disposable glove). If you feel a gentle suction, that is normal. However, if it seems like the crankcase is forcefully pulling your hand in, it indicates a potential problem with the crankcase ventilation (CCV) system.

Inspect the tube extending from the front of the crank case to ensure that it is not torn or damaged. This tube is connected to the crankcase ventilation (CCV) valve.

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