Bad MAF? Lean codes

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Oct 26, 2010 | 06:33 PM

AWC

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Joined: Aug 2003

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Bad MAF? Lean codes

97 4.0.Throwing lean codes both banks. P0171, P0174. The only symptom I have is a ocasional rough idle. Almost like it's running on half the cylinders. While it was idling real rough I unhooked the MAF. It smoothed out & idled fine. Is this a safe bet that the MAF is bad & causing the codes? I cleaned it twice didn't help. Is there a way to check it to be sure?

Oct 26, 2010 | 07:05 PM

Hank85713

Cargo Master

Joined: Feb 2002

Posts: 2,414

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From: Tucson USA

check for air leaks in the intake tube where the breather tubes hooks up etc. I had a air leak there and the maf went bad, but I think they are only around $50 at autozone.

Oct 26, 2010 | 11:26 PM

KhanTyranitar

Postmaster

Joined: Oct 2009

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Don't waste you money on parts store MAFs, get the genuine Motorcraft only. I've been through too many aftermarket units. My original lasted 160,000 miles, then I went through 2 aftermarket units, and it just didn't run right. Put a Motorcraft unit in, and it brought it right back and made it run right again.

I agree, check for leaks. Just because it runs better with the MAF unplugged doesn't mean the MAF is bad, it just means the MAF reading is bad, which can be due to either a bad MAF, or a leak.

Oct 27, 2010 | 07:48 AM

MikeB 88

Fleet Mechanic

Joined: Jan 2005

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Last time one of my vehicles threw both of those codes, it turned out to be a crushed and cracked PCV hose.

Oct 28, 2010 | 08:13 PM

AWC

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I will definitely go back with oem parts. That's all my boss will use on his work F550. I did tested the MAf By checking the signal & return wire with my meter. I read it should be .8v at idle. I got .65v.

I looked for vacuum leaks. Couldn't find any., I was going to do the intake gaskets until I unplugged the MAF & the idle smoothed out.