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Q: How can I check for vacuum leaks? on 2004 BMW 325i

A few weeks ago my service engine light came on. So I went to auto zone a borrowed there OBD2 scan tool. The codes displayed were P0171 & P174, system too lean in bank one and bank two. Next I read up on the error codes and I checked a few things. First I checked the air filter and it was filthy. The date on the airfilter was February 2004.....looks like air filter was Never changed, so I changed it. Next I cleared the codes with the OBD2 scan tool and the next day the light came on. So the next step I took was to clean the mass air flow sensor and that did not work either....I still get the same error code :-(. Now I need to know how can I check for vacuum leaks? I see no damaged hoses. Should I take my car to the BMW dealer? I'm still under warranty until may 2010, but I'd hate to get billed for something simple to fix. They wanted to charge me $130 just to check the codes.. :-/.
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This is all likely covered under the emissions warranty, so I wouldn't worry about it. As a matter of fact, you shouldn't be "cleaning" the MAF, this could void the warranty on that part, so it's a good thing you didn't do it! Right?
I would take this in to the dealer, they should address this for no charge, just make sure they inform you prior to any charges so you can decide before they do the work.
Thanks for the update, nice work Maria. Did you visually see the cracks, or were they found by another test method? How many miles do they have on them?
A few suggestions:
1. Purchase a high quality repair manual, for BMW I recommend checking out or
2. Be very careful using anything but the OEM air filters. These engine management systems are designed to work with the OEM parts, using other parts that are of different quality and built to different standards can interfere with the normal operation and even set Check Engine Lights.
3. If the vehicle is under warranty, especially an emissions warranty, consider having it repaired for free if it's covered.
Finally, not everyone will take the approach you have, but I admire you for it. It can be very intimidating dealing with these types of car problems, but you have a good approach to problem solving and that is very important.
Problem fixed for $50! I purchased and replaced both the upper and lower air intake boots, service engine light dissapeared. The upper air intake boot was cracked and the lower one did not looked good either....looked like it was dried up and ready to crack. Code p0171 & P0174 cleared.
Hi bretb.. basically I took off the air intake boots and looked them over. Thats when I noticed the lower boot had a 1/4 inch split and the lower boot looked like the rubber was dry and on the verge of cracking. The 325i had 57400 miles when I found the problem. My friend Dan works at BMW, and he told me that to replace both the upper boot and lower boots, the dealer charges $200. Im so glad I found it!! Im not a mechanic but I love my car so I read up on how to repair certain things. Next I plan to work on my own brakes ;-)).

*** Troubleshooting BMW 325i Codes P0171 and P0174 ***

If you ever get codes P0171 and P0174, I recommend checking and replacing if necessary the following:

1) Invest in an OBD2 scan tool (Auto Zone $60 on sale)or ask Auto Zone to check the codes for you (They do it for free).

2) Check the air filter and replace if dirty - $24 for OEM air filter at BMW dealer parts dept.

3) Check upper air intake boot and lower intake boot - $40 for both - I purchased both OEM parts at BMW dealer - parts dept.

Special note: Make sure you have a 6MM tool to remove the clamps. Might be hard to get in with a ratchet especially when trying to remove the lower intake boot thats attached to the throttle body. I used a small 6MM wrench. The hardest part was removing the small hose clamp that was attached to the lower boot.

Any reccomendations on tools I should have used, feel free to advise, so I can purchase some handy tools at home.

4) Finally, clear the codes with the OBD2 scan tool.


After I had replaced my air filter the Service Engine Soon light came back. So I called the BMW dealer and they told me it would cost $65.00 just to check the codes and find out where the problem was located and it would cost $200 for parts and labor to replace the air intake boots.

BMW dealers will NOT look at your car for FREE!!!!! Just to check for the problem is $65.00 (BMW dealer in Westmont, Ill charges $65 and Levin BMW in Schererville, Indiana charges $125--what a difference in price)!!!

So if you invest in that handy Scan tool, you will save lots of $$$$, because it will give you and idea where to locate the uses the same tool, but they will sell you some other crap saying they do other special tests.

Thanks bretb for your advice and info.
Hi again Bretb..

Thank you for all the info you sent me and I will purchase an OEM air filter directly from BMW.

My vehicle is under warranty until April 2010, but the dealer stated the air filter and upper and lower boots are not covered under my current warranty, but the MAF was. So in order to save the $65 service fee just to look at the car and the $200 to replace the air intake boot I took it upon myself to repair :-).

Thanks for all of your help and I plan on purchasing a repair manual. From now on ill use only OEM parts. :-)

Take care
If your lower intake boot is torn, it is possible that your pcv valve has gone bad also. Will recommend to replace pcv valve and all hoses coming off of the pcv valve. Will not recommend if you do not have the proper tools and time to get this job done. If you have some mechanical back grounds, then it will not take you long. If you don't, will highly recommend to take to BMW dealer.

Thank you

P.S. Using propane is not a good idea, the best way is to use brake cleaners that you can purchase at any local automotive stores. Propane is highly combustable when vehicle is running, brake cleaner will not combust when introduced onto or into the intake side while the vehicle is running.
Having a vacuum leak from a torn intake boot is not cover under the emmissions warrenty. It only covers defective parts such as an O2 sensor, cat. converter, or pcv vavle. But there is a limitation also depending on your location in the US.
Use a propane torch (open valve - without lighting gas, of course) and SLOWLY move torch nozzle along any intake manifold hoses and duct work. You need to be upstream of the MAF (Mass air flow sensor so that you don't get a false result when the engine inhales propane gas from the air filter box or air intake). If at any point, you hear engine RPMs increase, you have a vacuum leak. At this point you can hone in on the source of the leak. This will take a little practice and patience.

Disclaimer: Introducing propane into the engine bay may sound like a dangerous proposition, but in point of fact, it isn't, UNLESS you have an open flame or a lit cigarette in your mouth - be wise!!
i had the same problem today took it to autozone and they told me it was a vacuum leak so it could be a couple thing thats what they told me so first he told me to try spraying brake fluid all around the head gasket and hoses in if the engine would start shaking then theres where the problem could be but my problem was the gas cap replaced it and light when off.
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