Instructables

How to check and change a Mass Air Flow Sensor for a 1999 Subaru Forester

Picture of How to check and change a Mass Air Flow Sensor for a 1999 Subaru Forester
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This tutorial walks you through how I checked and changed my Mass Air Flow sensor using the tools available at TechShop San Francisco.  People usually say "I made it at TechShop!"  But I guess this really is more of a "I fixed it at TechShop!"

Tools you will need:
Security Torx Screwdriver set
Flathead Screwdriver
Multimeter (I used Techshop's Rigol DM3058 Multimeter, but a handheld will work just fine).
Mass Air Flow Cleaner (available at your local autoparts store)

The Mass Air Flow Sensor sits within your cars air hose and lets the cars computer know how much air is flowing into the engine.  This allows the computer to adjust to achieve an appropriate ratio of air and fuel (and spark) in a fuel injection engine.

On a 1999 Subaru Forester, the MAF Sensor is located on the passenger side, on the air hose that comes off of the air filter.  The one in the picture below has a blue stripe on the top.
 
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Step 1: Open Air Filter Cover

Picture of Open Air Filter Cover
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1) Undo the metal clasps on the Air Filter Cover (rectangular plastic box shape abbutting the passenger side.
2) Lift up on the cover.

Step 2: Unplug MAF Sensor

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There is a plug that attaches to the MAF Sensor.  This is what connects the sensor to the computer.  Unplug it by pressing down on the tab on the top and wiggling it until it comes free.

Step 3: Remove MAF Sensor

Picture of Remove MAF Sensor
The MAF sensor attaches to the air intake hose that runs between the air filter and your car's air intake using two security torx screws.  Unscrew the torx screws using the security torx screwdriver.  These screws are similar to regular torx screws except that they also have a small cylinder shaped nub sticking up out of the middle.  A security torx bit has a recess to fit over this nub.  You can find a set of these for cheap (under $10 at an autoparts store).  I just borrowed one from TechShop. Use the flathead screwdriver to help pry the MAF free of the housing a bit.
It's amazing how many car parts can last longer with routine maintenance. Thank you for sharing, I will try and track down my MAF Sensor on my honda.