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BMW - Solved P0171, P0174 and other fault codes by replacing K&N filter with OEM

1996 - 2003 (E39) - Bimmerforums - The Ultimate BMW Forum - forums.bimmerforums.com
vehicle: 2002 530i e39

Short Version: Constant fault codes (P0171, P0174 and others) related to lean mix, O2 sensors, MAF, etc. Thought the problem was downstream of intake. It wasn't. My K&N air filter was letting in too much air; replaced it with a quality OEM and codes went away and performance and mileage improved dramatically.

Long Version: Ever since purchasing my 2002 530i I've had nearly constantP0171, P0174 and other codes all associated with lean fuel/air mix in one wayor other.

- I cleaned, then replaced my MAF; performance improved a bitthen the codes returned.

- Ran a ton of cleaner through system, a little better butstill the codes.

- Replaced a cracked vacuum line, same thing.

Finally, checked for vacuum leaks with carb cleaner method -found a very small leak around VANOS but nothing major. Left the 02 sensors alone.

I didn't stop to consider that "lean" means itsgetting or detecting too much air and I also assumed that the problem must besomething involving or downstream from MAF.

SOLUTION: Upstream from MAF was my K&N air filter whichis designed to let in more air than the OEM that the various meters aredesigned to read.

So as a last resort before taking car in to the shop I replaced my K&N with a standard air filter (Purolator One). It was life changing! The car immediately improved: idle smoothedout, acceleration was more responsive, even vibrations coming from motor wentaway. And, the codes all cleared ontheir own. That is, in my case the K&N hurt performance.

Looking back at my previous BMWs, a 95 e38 and 98 e38, thesame problems persisted.

Might not work for your car but if you have some version ofa cold air intake, non-spec air filter etc and have not paired it with thecorrect MAF (for example, a Dinan CAI with a Dinan MAF) try spending $20 buckson a standard filter before wasting weekends chasing codes.

A final question as I close this long chapter: If"cold" air intakes are supposed to deliver more power, how comemotors don't generate more power in the winter compared to summer or eveningsvs day?

Press on regardless,

Ice Planter
Date: Oct 13, 2017    Labels: BMW


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