Mass airflow sensor
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New User
Joined: Oct 2010
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Mass airflow sensor
Is there any way to rule out this sensor? I have already cleaned it. My truck runs very rough at idle but runs great other wise, also the rough running has gotten worse as time goes on. What else could be causing this problem? P171, p174
2004 expedition V8
Thanks
2004 expedition V8
Thanks
Senior User
Joined: Sep 2009
Posts: 263
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Check to see if the IAC is working properly and if you have a scan tool that can read data, hook it up to the truck and read the output from the sensors to see if they are in spec. Normally I have seen these codes go off because of a vacuum leak. I would check around the intake and throttle body to see if there is a leak. You can hook up a vacuum gauge and see what its running at idle. Even a very small leak can set these dtcs off. My friends truck set this code because his valve cover gasket had a very leak. If you don't have a scan tool go to your local auto parts store and see if they will read it for you, that is if their scan tools can read the data.
Logistics Pro
Joined: Jan 2001
Posts: 3,740
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From: Central NYS
P0171 and P0174 indicates the PCM is driving both bank's fuel injectors full rich - LTFT (Long Term Fuel Trim) has exceeded ~ +25%. It is trying to get rid of the excess oxygen in the exhaust. That excess O2 comes from one of two sources - either a vacuum leak between the MAF and the intake valve, or, incomplete combustion caused by an insufficiant fuel supply (read weak fuel pump, plugged fuel filter, poor fuel pump relay, etc.) Look at the freeze frame data to see under what condiction the code was set to narrow down the culprit - if the codes set under load it is probably fuel supply - if under light load/idle condictions it is more than likely a vacuum leak.
Senior User
Joined: Jul 2003
Posts: 270
Likes: 1
From: tampa bay area
I just had this on my friend's 03. Same codes and symptoms. It was a bad PCV elbow at the back of the intake/throttle body as pdq suggested. You have to replace the entire hose which you can only get from the dealer. Surprisingly, it was only around $32. Or you could do the old heater hose and hose clamp deal to get by if this truly is your problem.
Good luck.
Good luck.
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fjerstadt
Explorer, Sport Trac, Mountaineer & Aviator
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Jun 3, 2010 08:12 PM
