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Discussion Starter · #1 ·
I know, I know, there are a dozen or so threads related to this. believe me, i've checked.
from what i read, many members suggested replacing the spark plugs and connectors. my car does have 145,000 miles and even though I changed them at around 90,000 i figured that a change was due.

I changed the plugs and connectors today and i'm still having the same blinking check engine soon light. i plugged my scantool up and all i'm receiving in errors is "P0171" "too lean in bank 1"

is this my O2 sensor that is out. I even sprayed cleaner on areas of the manifold and MAF to see if there was any leaks..none. My car is idling rough and I'm clueless at this point as what it is. i'm sorry if this sounds dumb but, could the O2 sensor really cause this?


any advice would be most appreciated..
 

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Freude am Fahren
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MAF or vacuum leak. There are other parts that work. Check the OEM part number (i.e. Bosch or Siemens, whoever made it, not the BMW part number) against other parts. A search of the forums will turn up a few useful threads.
 

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Seek to understand,^Value
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If it is the MAF, these from the VERY best of E39 Links, may help:
- MAF CLOGS: the mass air flow sensor (MAF) and idle control valve (ICV) require periodic cleaning (1) (2)

As for replacements, look in the same place:
- Buying a replacement MAF cheaper than the BMW MAF (RangeRover MAF) (VW MAF) (Hyundai MAF)

Note: Somehow we "lost" the VW link so I ask the OP to search for the equivalent VW MAF and post it back here so everyone benefits.
 

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livin the 'Fest
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i'm not sure on the 540's but i know that on the i6's the o2's are interchangeable, if yours are, switch them, clear the code and see if the code moves with supposed bad o2, if it does then you fixed your problem. if you get the same codes then kept searching out the problem. a intake leak could also set off the code.
 

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I believe it was a Jetta or Golf. If I can find the box, which I believe I still have, I'll post a pic of the part number from it for reference. Prices may have jumped a bit since I bought it 4 years ago but not by THAT much. I got mine from a dealer too!.
 

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Seek to understand,^Value
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I'll post a pic of the part number from it for reference.
That would be useful to us for now, and in the future ... since you can rest assured this question will come up again (and again).
 

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Discussion Starter · #11 ·
guys thanks for all the info...i went ahead and bought a new MAF (range rover) which is also the same spec for 2000 540i from ebay, and pre and post cat o2 sensors from rock auto

MAF-90.00
13 477 pre-cat: 60.00 each x2
13-477 post-cat ;roughly 90.00 x2

i got hit for about : close to 400 which doesn't seem bad considering what i've read from previous post and what was spent.

when checking to see if the intake manifold is leaking or for vacuum leaks, is there any good tutorials out there? i ran a check, but i may not have gone through the right methods.,.,,
 

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I have the same code po171. Engine light doesnt blink, but it comes on and off whenever it feels like it. I replaced valve cover gaskets, intake gaskets, throttle body gaskets, all the gaskets in the intake tube. Still throwing codes. Finally I found my leak, it was the 2 upper timing covers in front of the engine. Good luck.
 

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Discussion Starter · #14 ·
I have the same code po171. Engine light doesnt blink, but it comes on and off whenever it feels like it. I replaced valve cover gaskets, intake gaskets, throttle body gaskets, all the gaskets in the intake tube. Still throwing codes. Finally I found my leak, it was the 2 upper timing covers in front of the engine. Good luck.
Qwiksilver, what do these look like, it seems when i get a handle on one problem, i'm asking questions for a new one and i'm sure it's probably pretty obvious, but i'm not quite certain. i have crc cleaner, is this what you used to determine the leaks?
 

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Discussion Starter · #15 ·
1). P0171 = Lean = cheapest and most importantly smartest thing to do first = check for vacuum leak.

You just spent $400.00 on "stuff"

Lean = either too much air or not enough fuel

Lean codes = see #1 above.

Happy Valentines Day to Chivas.
I did actually spray crc cleaner to check for vacuum leaks, but i didn't hear any significant changes in the engine when i did it....may have sprayed in the wrong places.....:dunno:
 

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I did actually spray crc cleaner to check for vacuum leaks, but i didn't hear any significant changes in the engine when i did it....may have sprayed in the wrong places.....:dunno:
Smoke Test is the only 'real' way to find a vacuum leak.

FYI: A a leaking valve cover gasket will offer you oil and that oil shows you that if oil is getting out, you have a leak.

Stuff like that etc.

Again, you have a P0171 which is "Lean Bank One" and if you Googled tm it you'd see:

http://webcache.googleusercontent.c...:http://www.obd-codes.com/p0171+P0171&ct=clnk

So cleaning a MAF *might* make sense indeed.
So doing a smoke test *might* make sense indeed.
Then consider fuel pressure as well (though a bad fuel filter would impact more than one bank).

Purchasing a MAF is an odd approach.
 

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Discussion Starter · #18 ·
Smoke Test is the only 'real' way to find a vacuum leak.

FYI: A a leaking valve cover gasket will offer you oil and that oil shows you that if oil is getting out, you have a leak.

Stuff like that etc.

Again, you have a P0171 which is "Lean Bank One" and if you Googled tm it you'd see:

http://webcache.googleusercontent.c...:http://www.obd-codes.com/p0171+P0171&ct=clnk

So cleaning a MAF *might* make sense indeed.
So doing a smoke test *might* make sense indeed.
Then consider fuel pressure as well (though a bad fuel filter would impact more than one bank).

Purchasing a MAF is an odd approach.
I actually did google it, but sometimes when we are in a bit of panic as to issues that arise, we tend to overlook websites that give us the in depth information that we are needing. I appreciate the link, that explained it quite well....if it is a vacuum link, then i may have bought these parts prematurely.......
 

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Seek to understand,^Value
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i have crc cleaner, is this what you used to determine the leaks?
IIRC, how to test for leaks is described in links in this the VERY best of E39 Links thread:
- How to diagnose a BMW E39 engine misfire (1)

It even comes with a leak-testing video IIRC.
 
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