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Discussion Starter · #1 ·
hi all. I've been helping my friend with his 2001 325i for about a year now. it has had a ton of problems including a check engine light that just won't quit. i have managed to slowly eliminate most of the codes but this last part has been killing me and he needs to pass smog by january here in cali.

so last night i hooked him up to autoenginuity. I clear the codes and what keeps coming back now is o2 sensors have reached their threshold and system is lean. car will idle pretty normal for a while. once you try to drive it it will throw the check engine light and go into limp mode. after that happens it will have codes cylinder #* misfire with lean mix. it will happen on any and all cylinders. we have replaced faulty ignition coils, maf, intake boot, o2 sensors, vacuum lines, fuel pump, fuel filter, etc slowly taking codes away but that is what I'm at right now. I'm thinking theres a vacuum leak somewhere, possibly the intake manifold gasket. either that or dirty fuel injectors. something is causing the car to run lean at all times. anyone care to chime in with some ideas?
thanks
 

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Is it on all cylinders? Or just a specific one? Also how does the car drive when it's lean? Does it hesitate or anything?
 

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Discussion Starter · #3 ·
it will happen on all cylinders but won't give me codes to all at the same time. they will vary. the car drives horribly. it stumbles and dies just about every time its driven.
 

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Did you check these vacuum lines? They are connected to the main system, and can cause errors. I found that mine had a leak, and part #3 was the source. It is a rigid plastic hose, and it was full of cracks:
http://realoem.com/bmw/showparts.do?model=BN53&mospid=47713&btnr=11_2203&hg=11&fg=45
It was also causing my blower to sound much louder, because the valve was not opening. I did a quickie fix, and the codes cleared. I was also getting the same O2 sensor codes as you. It has been about 10 day, and so far, mine seems OK. This may not apply to you at all, but I thought I would mention it..
 

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Did you check these vacuum lines? They are connected to the main system, and can cause errors. I found that mine had a leak, and part #3 was the source. It is a rigid plastic hose, and it was full of cracks:
http://realoem.com/bmw/showparts.do?model=BN53&mospid=47713&btnr=11_2203&hg=11&fg=45
It was also causing my blower to sound much louder, because the valve was not opening. I did a quickie fix, and the codes cleared. I was also getting the same O2 sensor codes as you. It has been about 10 day, and so far, mine seems OK. This may not apply to you at all, but I thought I would mention it..
He is absolutely correct! Look my thread on xi forum.. I just finish doing my vaccum lines sir. Search!!!!!go change it.. It's our problem solver!! Trust me ;)
 

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do a smoke test to check for a vacuum leak. easiest way to quickly check the whole vacuum system.
i doubt it spark plugs. they wouldn't throw a code, although they can definitely make the car run bad.
have you checked compression?
also is it possible the 02 sensor could actually be bad making the car think it's lean which makes it run like crap.
 

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unplug the maf (while the car is off!) and drive it without it plugged in. does it run any better? worse?
 
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