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#1 (permalink) Old 09-11-2012, 05:35 PM
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MAF or vacuum leak

Good afternoon everyone. I have a 2005 525 with a little over 77,000 miles. Last night I started it, and when it idled down, it started shaking, and I could hear that all cylinders were not firing. The service engine soon light came on, so I took it down to AutoZone today to have them pull the codes. Here's what they gave me:

1) 0301 - cylinder 1 misfire. Probable causes: plugged or faulty fuel injector, vacuum leak, or engine mechanical condition.

2) 0171 - system too lean, bank 1. Probable causes: faulty MAF sensor, large vacuum leak, low fuel pressure, plugged injector or cylinder misfire.

3) 0174 - system too lean, bank 2. Probable causes: faulty MAF sensor, large vacuum leak, low fuel pressure, plugged injector or cylinder misfire.

So, from this info it would probably be either a vacuum leak or MAF since BOTH banks are running lean, right? Which would be the more likely culprit, MAF or vacuum leak? I've read more threads about bad MAF than vacumm leaks, but I don't want to drop a bunch of $ on a new MAF sensor if it's not broken.

If you are leaning towards vacuum leak, are there any usual suspects on 5 series I should focus on first? I saw on one thread that there is a little corrugated hose on the lower boot, under the air intake. Any other places I should look?

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#2 (permalink) Old 09-11-2012, 05:41 PM
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Guess I should have read the post right underneath this one first. I will unplug the MAF and see if it idles better.

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#3 (permalink) Old 09-11-2012, 06:11 PM
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Okay, it's not the MAF sensor. I unplugged it and the car still idles like crap. Now on to vacuum leaks? Or am I chasing the wrong rabbit here?

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#4 (permalink) Old 09-12-2012, 12:55 AM
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Start with looking for a vacuum leak. When their is unmetered air entering the system the computer cant compensate for it properly.

Misfire's are normally plug related. I would check the plug in that cylinder, and fif it looks okay i would swap it out with a plug from a different cylinder and see if the code goes away. If it doesnt, then the issue is something else.


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#5 (permalink) Old 09-12-2012, 08:59 PM
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Got in the car this morning, cold engine, no problem. No unusual idle or sounds coming from under the hood. Got to work 30 minutes later, hot engine, and crappy idle had returned. I could also hear a whistling / sucking sound so I popped the hood and had a look. The whistling is coming from the connection with the arrow pointing to it. The second pic is a close-up of it. When I turned the engine off, it continued to make a dying whistle for 2-3 seconds afterwards. Got back in the car 9 hours later, cold engine, no problem. Pulled into the driveway thirty minutes later, same rough idle and whistle. I sprayed carb cleaner on the connection and the idle sped up, so I've obviously got a vacuum leak. However, realoem.com does not show a hose diagram for my model, so I don't know what the two hoses that attach to the connection are called (or their part numbers) to order new ones. Anyone out there no where else I can look to find the part numbers for these specific hoses?

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#6 (permalink) Old 09-12-2012, 09:00 PM
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Whoops, forgot the pics.
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#7 (permalink) Old 09-13-2012, 12:44 AM
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What engine do you have? M54 or N52?

I put it in as N52, and this is the diagram i got back. To me, it looks like part #7.

Intake manifold system BMW 5' E60, 525i (N52) ? BMW parts catalog


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#8 (permalink) Old 09-13-2012, 07:30 AM
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I have the M54. I went to that website and looked at the diagrams for the M54, and still no pics of the hoses that attach to the "angle connector" found on the link above for the N52 engine. They are molded hoses with special connectors on the ends, so I can't simply cut a length of rubber hose from my stock in the garage.

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#9 (permalink) Old 09-16-2012, 11:52 AM
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After getting much more precise with the carb cleaner, I realized that the leak was not where I originally thought it was. It was actually the hose that runs from the top of the oil pan at the dipstick tube up to the bottom of the intake. It had a nylon "protective" sleeve on it that really does nothing. The hose ended up being split underneath from constantly rubbing on a bolt head on the engine block, but the split could not be seen because of the nylon sleeve. I went down to the parts store and bought a replacement section of hose, and a larger diameter piece too to slide over the replacement section to act as a protective buffer. The hose simply pulls off at the branch on the dipstick tube, and the plastic connector that attaches to the intake can be pulled off from the old hose and put on the new hose. Went back to Autozone, borrowed their ODBII scanner, and cleared the stored codes. No more service engine soon light, and no more rough idle.

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#10 (permalink) Old 09-17-2012, 12:52 AM
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Glad to hear you got it fixed. Sometimes those hoses can be a major PITA.


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