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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > General E90 Sedan / E91 Wagon / E92 Coupe / E93 Cabrio > Codes P0171 & P0174



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      04-17-2012, 07:18 PM   #1
tpafl328
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Codes P0171 & P0174

My check engine light came on today with these codes P0174 & P0171. For the past week or two I have been having problems with the way my car has been driving. I took it to the dealer and they weren't sure what it was but that it might be crankcase valve and to come back when the car is completely messed up. The car rpms jump up and down and sometimes make a loud whistle noise. Both of these symptoms aren't always present, most of the time it drives perfect. I'm getting frustrated since the dealer were no help. So... does anyone have any suggestions of what this could be? Is it the crankcase valve? The dealer said that if it is the crankcase valve that the valve cover need to be replace since its now integrated in the valve cover. Is that true? Also my car was previously flooded a few months ago, not sure its related or not.
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      04-17-2012, 07:22 PM   #2
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Most likely a vacuum leak or MAF sensor problem, both are fairly common on that engine, good luck with the repair.
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      04-17-2012, 07:26 PM   #3
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Would vacuum leaks or MAF sensor cause the car to make a whistle noise. Whenever it does that sound, it starts off low and then gets really loud.
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      04-17-2012, 09:51 PM   #4
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Originally Posted by tpafl328 View Post
Would vacuum leaks or MAF sensor cause the car to make a whistle noise. Whenever it does that sound, it starts off low and then gets really loud.
Vacuum leak will do that. MAF sensor probably not.
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      04-17-2012, 10:16 PM   #5
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The check engine light is no longer on. It turned off on its own. This is the second time it's done that. I'm worried that somehow this will damage the engine. I don't know what to fix and neither does the dealership lol
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      04-17-2012, 10:18 PM   #6
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I'm gonna try and find a good independent place to see if they can figure it out.
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      04-17-2012, 11:28 PM   #7
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While the car is idling, open the hood and listen for any whistling sounds. If you do, that is a vacuum leak. You should also perform a smoke test at a shop, which will send white smoke through the air intake and look for where it comes out to find the vacuum leak. If it passes the smoke test, then at least the vacuum leak can be eliminated and you can move on to check for other causes of the system being too lean. It could be MAF, as suggested, and cleaning it with a CRC electronic cleaner spray or MAF cleaner might work. It could also be a restricted fuel delivery problem- e.g clogged injectors. If I were you- I would clean the MAF first, visually inspect and listen for whistling sounds and pinpoint the area where unmetered air is rushing in, and throw in a bottle of techron in the fuel tank to clean out the injectors. These are the easiest things to try first. If no success, then you can look into replacing the PCV (positive crankshaft valve).

Other things to look at after ruling out the above would be dirty fuel filter and fuel pump- easiest way to check would be to measure fuel pressure. The filter is built in into the tank and not easily replaceable (but not impossible).

At some point, you should also replace the oxygen sensors (they are due at 120K miles per BMW).

Last edited by queensfield; 04-17-2012 at 11:46 PM.
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      04-18-2012, 09:04 PM   #8
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Thanks for the reply! I'm gonna try this stuff out and hopefully solve this problem.
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      04-19-2012, 11:39 PM   #9
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Whistling noise in combination with those codes is pretty much an air intake leak after the MAF. Typically this would be the air intake boot (upper and lower) going to the throttle body & idle air control valve.
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      05-17-2012, 06:07 AM   #10
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Hi, I recently began experiencing similar symptoms, perhaps not as severe. Not seeing any codes yet. No jumps in rpm either. Today my car runs fantastic, no indication of a past problem whatsoever, but I expect the issue to come back.
http://www.e90post.com/forums/showthread.php?t=691932
In addition to what was suggested to you here, there are replies to my post that lean towards what your dealer is thinking.
Thanks for suggestions made here and any others in the future.
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      12-19-2016, 08:46 PM   #11
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Did anyone ever confirm these issues as being MAF sensor or a vacuum leak? Or both?

I threw both of those codes today on my e90...and weeks ago I had that whistle problem and my engine shut off as I was turning left going maybe 20mph...but never got a check engine light and after turning the car off and back on.
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      12-19-2016, 10:49 PM   #12
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A dirty MAF sensor can cause too lean codes but dirty or clean MAF Sensor cannot make the car whistle. Whistle and lean code indicate vacuum leak.
A torn crankcase ventilation valve membrane can cause vacuum leak. You can test this by placing your finger on the nipple coming from the crankcase ventilation valve while engine is running (after removing the dust cover cap on it). If it is sucking vacuum on that nipple it is torn.
A dirty stuck crankcase ventilation valve can also cause vacuum leak, but from the crankshaft seals. Stuck valve allows too much vacuum to be pulled on the crankcase and then air rushes in from the crankshaft seals.
To test this, try to open the oil fill cap while engine is running. If it is very difficult to open due to higher than normal vacuum on the crankcase, then you found your problem.

If not these two, then you can have some other vacuum leak somewhere after the MAF sensor, but these won't cause
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      03-06-2017, 09:24 PM   #13
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I have both those codes but no whistling at all only a fluttering sound @ two a second that is new its fairly constant but it has disappeared for a few seconds then returned while at idle.
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      03-07-2017, 12:36 PM   #14
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On the older BMW's the whistling noise "usually" was due to a torn air boot right after the MAF. That big boot would deteriorate in time. Also, another culprit was the CCV valve and ancillary hoses - a PITA to replace. Both types of failure would trigger that code - air leak (lean codes). And would have the whistling noise associate.

With the N52 engine, the CCV was replaced with an integrated PCV valve, which unfortunately also deteriorates in time. The only solution would be to change the valve cover, but this is an expensive fix, especially if there's no apparent VCG failure/leak. Fortunately, there are 2 places that sell the PCV valve. The replacement part is cheap, and it involves a little careful work. I think the risk is worth it: a couple $$ vs a new valve cover. If you break the valve cover trying to do the fix, it means the valve cover was almost "cooked" anyway and was in need of replacement. Below are the links to these 2 sites that source the original part the same BMW does. They also have instructions how to remove the failed part and replace with new.

Dr. Vanos

Russian counterpart

P.S. both sites have also DISA repir kits for N52 engines. Also an alu cap for the PCV valve in case you want to replace the OE plastic part.



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Last edited by doru; 03-07-2017 at 12:45 PM.
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