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Old 02-10-2013, 06:56 PM   #7
Registered User
Join Date: May 2009
Location: Silicon Valley, California
Posts: 92
My Ride: 04 325i & 00 323Ci
Cool P0171 and P0174 Codes in E46

In my 2000 323Ci (155k miles), 2001 Xi (with 232k mi), and 2004 325i (96k mi), we have to pass a smog test every other year here in California. The 2001 and 2004 are running fine, but showing the P0171 and P0174 'lean' codes and so won't pass smog. Despite the tears and totally shot hoses throughout the motor (my son bought it that way) and a smooshed front corner, the 2000 is not throwing any codes, which makes no sense, but hallelujah.

ALL THREE had a tear in the bottom of the ribbed part of the intake tube after the MAF sensor, which is caused by lifting up the cover of the air filter over the years. It is easy to check: take off your air filter cover + MAF by loosening the adjacent hose clamp, and shine a light around the tube in a dark garage while bending it upwards. The tube is about $28 online, and the 2004's motor had a bigger tube than the other two. It is easy to replace, compared to most other BMW repairs.
BTW- Caulking and duct taping the tube's cracks doesn't work, since so much wiggling is involved to get the MAF Sensor and air filter back on.

While you are there, spray MAF Cleaner (about $5 at AutoZone) on the delicate MAF sensor inside the unit and check that the rectangular flap valve stuck into the engine behind the tube is working. A few bolts and it pops right out. It tends to get gummed up with gunk so it doesn't move easily. Just clean the gunk off with whatever is handy. I used WD-40, a flathead screwdriver to scrap the edges, and a rag.
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