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Old 04-04-2009, 02:22 PM   #1
MerflinFE
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Join Date: May 2008
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My Ride: 2001 330CI Coupe
How I beat the PO171 and PO174 codes

For reference I have a 2001 330Ci Auto-Coupe with just over 50k miles:


I wanted to share with some of you how I beat these codes. I have read on many of the posts on these that they come up and people say that can't figure them out and then the posts end up disappearing or becoming Zombies later on.

Both of these codes together told me that there was a lean condition through out the intake and exhaust system of the car. Only having one code would have made it harder to track down, but ultimately not impossible. Since the condition was in the whole system I started thinking about what was common to the whole system. The only thing I could think of was the vacuum system. The vacuum system would have allowed unmetered air in or out of the system depending on load causing ( in my case) the light to go on for a week or two and then go out for a day or two.

I started poking around in the engine bay after having a professional BMW place take a look and tell me what I already knew (it could be...this or that blah, blah, blah). I took all the covers off the engine and removed the panels off the firewall ( took about 5 minuets with a T20 screwdriver and 10mm socket).

At the back of the intake manifold there are no less than 5 vacuum points going to different sensors and locations around the engine bay. Looking closely I found a vacuum cap that was cracked and obviously letting unmetered air into the system. I started to feel around in that area and found that a few lines were cracked, and one just disintegrated in my hand into a powdery black substance.

This being not the ideal situation, I found the proper vacuum hose at the autoparts store, bought 20 ft of it and went to work. If you take your time you will find all the lines. I replaced ALL of them as the area was tight and a pain to get to. After I was done I went back to the autoparts store, grabed the code reader and read out the car. The only code left was a PO128 code that was for the thermostat reading out of range. Easy fix for later. I cleared the stored codes twice (out of spite), and haven't had one return yet.

I didn't realize how much power the car had been missing out on. It's MUCH more responsive. The idle is now completely smooth and rock solid at around 650 rpm after the car is warm. It's a shame I'll need to sell it soon, but I have a family on the way when I get married in May.

I hope this helps someone out there with these PO171 and PO174 codes. I know I would have appreciated this post while I was trying to wrap my head around this problem. The key to it is a visual inspection of every inch of vacuum line. Bring a mirror and a person with small carney hands if you can find one.

- Stephen

Last edited by MerflinFE; 04-05-2009 at 04:16 PM.
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Old 04-04-2009, 03:34 PM   #2
Dan99
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Nice write up.
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Old 04-04-2009, 03:48 PM   #3
wasp9166
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selling your car to get married , your a better man than i am bud
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"Mommy and Daddy are getting a divorce now because wasp9166 had to piitb with Mom."
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Old 04-04-2009, 03:49 PM   #4
Dannyncc
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can show picture?
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Old 04-14-2009, 01:29 PM   #5
Lemonsqr
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can show picture?
Show pictures of what? vacuum lines?
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Old 04-20-2009, 11:10 AM   #6
kwikt
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Don't forget the vac line on the fuel filter regulator. Thought the car was done throwing codes till yesterday. It caused all kinds of codes plus my wife barely made it home. The line was totally rotted!!!! When this happens it shuts off fuel to the engine.

Kevin
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Old 04-20-2009, 11:49 AM   #7
vminev
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Awesome... Im gonna do th is as soon as school is out (may 10th) I have had those codes for a year now and I couldnt figure out how to get rid of them... Thanks
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Old 04-20-2009, 11:50 AM   #8
giver13
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Pics of the points where in the engine bay these lines are located??? Id like to check mine but dunno where to look
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Old 04-20-2009, 11:55 AM   #9
MileHiXi
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Show pictures of what? vacuum lines?
The fiance.
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Old 10-30-2009, 04:47 PM   #10
Jha3d33 330i
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I got the same issue..Let me know if you find out.
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Old 10-30-2009, 06:07 PM   #11
Chriztofor
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For most BMW problems start off by reading your codes using a peake research tool. Note, as mentioned by other members, although Autozone checks your codes for free they use a generic OBDII tool that does not have the BMW specific fault codes.
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Old 11-18-2011, 02:42 PM   #12
druggrepp
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broken vacuum line throwing codes

My black beauty started stumbling and dying, I put a new fuel filter on it, $79 with regulator and the hose going to it was cracked too.
The stumbling has gotten better but NOW i know where to look before i try the oil seperator and icv again.
Thanks for the post.
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Old 11-18-2011, 03:01 PM   #13
lsteg
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worthless seems like a bit of a stretch
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Old 11-18-2011, 03:15 PM   #14
SweTurbo
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Vacuum lines i can recall are :

Intake after TB:
Fuel pressure regulator(323/328 is on front of fuelrail , 325/330 is integrated in fuel filter)
Purge valve (sits underneath the manifold and runs to inside of wheel arc, connector here breaks often)
Brake booster(Big hose from under manifold)
Before TB :
Brake booster for WOT line

On the side of the manifold there are 3 connectors stock all of them are capped as far as i know.
Big one isnt even drilled into the manifold(atleast i couldnt get any readings from it)
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Old 11-18-2011, 05:36 PM   #15
jdstrickland
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I'm sorry, the link between getting married and selling the car is what? Unless you have some of your own, and she brings some of hers, I don't see how marriage and BMW have to be exclusive of each other. Your car can easily hold you and her, and a carseat. I'll admit that putting the carseat in can be a huge pain in the ass, but the solution for this is to have a carseat for your car and another for her car. That way the carseat goes in once, and never moves.
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