Wingless Wonder

iTrader: (7)

Replacement procedure may be similar for other Impreza models and years.

1) Remove two fasteners retaining air cleaner snorkel to radiator support. Carefully wriggle snorkel until it pulls free of the fender panel.

2) Loosen two hose clamps and remove connecting elbow from MAF (mass air flow sensor) and airbox assembly. Note position of cables and tubing that clip to the elbow and airbox. Remove wiring harness connector from MAF.

Wingless Wonder

iTrader: (7)

3) Remove two fasteners on lower frame rail that retain the air box base through rubber vibration mounts. Use care not to drop the fasteners.

4) Remove air box either intact, or by removing cover and filter first by unsnapping the two spring clips that retain the cover.

Wingless Wonder

iTrader: (7)

5) Note air filter element sealing surface on right-side edge - it has been crushed by improper installation and will not provide a good sealing surface. The cover's tabbed edge was not properly installed on the air box, allowing unfiltered air to pass into the engine.

Wingless Wonder

iTrader: (7)

6) The cause of improper installation of the filter element is the tabbed air box cover that is hard to see during installation. Note how the tabbed edge on the cover should fit under the lip on the air box itself.

7) The trick to trouble-free filter replacement is to remove the entire air box and replace it completely assembled with cover in place.

With the air box on the ground or work surface, place the new filter element into position. There is some wiggle room when the filter sits in the air box. Pull the filter element away (in the direction of the arrow as shown in previous post) from side where the tabbed cover fits into the air box, creating a gap as shown.

This is the area that commonly crushes the filter element because the filter slips too far underneath and blocks the cover tabs from properly seating under the edge.

Replace the cover, carefully fitting the two tabs under the air box edge and making sure it isn't crushing the filter sealing surface. If the filter seal sticks out a bit on the opposite side as you close the cover down, just push it gently back into place with your fingers or a small screwdriver. Snap the two clamps to lock the cover into place.

Wingless Wonder

iTrader: (7)

The air box can be re-installed by carefully maneuvering the assembly underneath the vacuum hoses and working it over the plastic tubing in the fender. Fit the locating grommet into the corresponding hole in the fender. Replace and tighten air box fasteners to 25 ft. lbs.

Route vacuum hoses through their retaining clips on the air box assembly. Cruise control throttle cable must be routed above the MAF elbow when re-installing. Re-install MAF elbow, orienting screw clamps so that the worm gear does not rub on any other parts.

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0==WW==0
"…axles of evil…" - george w. bush

Mulder

Good writeup, but I've never removed the airbox to R&R the filter. It can be removed just by popping off the clips and lifting the top cover. When replacing, I hold the filter up in the top cover part (rather than laying it in the bottom), this makes it easier to get the bottom tabs in place and then the cover can be lowered into position and the clips fastened.
Also it should be noted that failure to latch the tabs can in some cases cause a P0171 lean condition code to set.

Wingless Wonder

iTrader: (7)

Good tip, Mr. Mulder, thanks!

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0==WW==0
"…axles of evil…" - george w. bush

Boost Addict

This is awesome... any chance it can be stickied????? It would help a LOT of people a great deal... Thanks for your efforts! awesome description and pics!