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Old 04-19-2005, 12:20 AM   #1
Scooby Specialist
Member#: 55011
Join Date: Feb 2004
Location: New England
1999 Legacy Outback

Cool How To Replace The IACV Gasket (Idle Air Control Valve)

After struggling with the reattachment of the IACV to the throttle body after cleaning the IACV, I thought I would post a quick write-up of how, after removal, the IACV can be best reattached. Feel free to post suggested changes or corrections to my thoughts below. This “How To” incorporates my own experiences with ideas, suggestions and information posted by Unabomber, Overdose, WRX3, and others.

Background Information
The IACV is the “Idle Air Control Valve,” or more fully, the “Idle Air Control Solenoid Valve.” The IACV directly affects idle conditions, RPM in particular. On cold starts, the IACV sends rpm’s higher than on a warm start. Irregular idle conditions may be the result of a dirty IACV sensor. Search under Unabomber’s name in this forum for details on cleaning the IACV. Removal of the IAC is covered on page 36 of the DOHC Engine service manual, for those that possess the manual.

Removal Tips

As shown in the picture below, the IACV sits on top of the throttle body. In this picture, I have replaced one screw (left lower corner) with a hex-socket cap screw, while the other screw (right upper corner) has been removed.

As indicated in Unabomber’s cleaning instructions, I had best results in removing the two stock screws that attach the IACV to the throttle body with a large, flat-head screwdriver as opposed to a phillips-head screwdriver. These screws are VERY soft, and you can strip them very easily, so take care when removing them.

WRX3 has also found success with this screw removal technique: Attach a small pair of vise grips to the heads of the screws, just enough pressure to slightly indent the metal. Turn the vise grips along with turning a phillips head screwdriver at the same time. It will break the screws loose 101% of the time with EASE. If you're careful and your "small" vise grips have a flat section at the tip of the teeth, you can barely see the indention on the heads of the screws. Larger vise grips work but it easier to eat up the screws. If you don't have a vise to hold the TB, break them loose while the TB is still on the car.

Have A New Gasket Ready

The IACV gasket is fragile, but what is more frustrating is that it actually expands under vacuum/pressure and temperature. As a result, it is possible that the old gasket has expanded so much that it is impossible to get it back into position once you have removed the IACV. You cannot know the condition of the gasket before removal of the IACV, so a good safety precaution IMO would be to have a new gasket standing by just in case.

The part number for the IACV gasket is 22659AA120. It cost me $6 from Exeter Subaru in NH in person, but I could probably have gotten it for less from online.

This picture shows how the old gasket expanded over the left-side of the gasket housing. It also shows where I pinched off a section trying to reattach the IACV.

This picture shows how much larger the old gasket is compared to a fresh gasket.

Seating And Sealing The Gasket
It is important that the IACV be properly sealed. As you can see from the pictures above, an improper seal will allow coolant from the throttle body coolant lines to flow INTO your intake. Assuming you are using a fresh gasket, insert the gasket in the gasket grooves on the top of the IACV. As explained by Overdose in other posts, the gasket will look slightly too small. This is normal, and it will expand with heat, time and vacuum. Here is a shot of the new gasket ready to go:

Once the gasket was in place, I closed the IACV back onto the throttle body (see the next section below). After the two bolts (I replaced the screws) had been torqued down, I reset the ECU (the manual says to do this; not sure if it is necessary, but figured it would not hurt). I then primed the fuel pump 3 times, for two seconds each time (I read this as part of Unabomber’s IAC cleaning instructions). I started the car, and let it idle for about 10 minutes. This allowed the gasket to slowly heat up with the throttle body.

Following good advice from Overdose, I then took the car on a 10 mile freeway drive STAYING OFF boost, which is harder than you might think. Our cars really want to stretch their legs at all times. But I wanted the engine bay to get warm with highway-rpm’s (yes, it was flush with highway-speed-airflow, but anyway…) while the vacuum of running without boost would force the IACV gasket to expand.

After driving for 10 miles, I stopped and let the car idle for another 5 minutes. I checked the IACV for any outside coolant leaks, and it appeared fine.

I then turned off the engine, and left the car to buy some supplies at Home Depot (not a relevant step in this How-To ) After about twenty minutes I returned, then started the car up. I drove back to the freeway, and, to see if the gasket was now sealed, applied boost. Then I applied more boost. After each application, I looked out my rear view mirror for any tell-tale clouds of white smoke that would indicate coolant had entered my air intake. No smoke. I then slowed down a bit, and did a nice healthy WOT run. All was fine. I continued to drive aggressively for the rest of the way home.

Reattaching The IACV
As indicated above, the screws used to attach the IACV to the throttle body are VERY soft. I stripped one when I was reattaching the IACV trying, and failing, to reuse my old gasket. Thanks to WRX3, who pointed out to me that the screws are 5 mm by 20 mm long, I went to Ace hardware and bought two M5 (5mm) 20 mm long cap screws with hex sockets. You can see one of these in the lower left of the first picture. The stock screws come with both a lock washer and a larger flat washer. I was unable (not sure how they got the flat washers on the screws to begin with) to remove the flat washers from the stock screws, so I used a small lock washer with each cap screw/bolt. I omitted using a flat washer with each cap screw/bolt, which meant that they were slightly longer than the stock configuration. That did not, however, prove to be a problem.

The torque specification for the stock screws is 2.1 foot-pounds. Not having a low-torque torque wrench, I used a small hand-held allen wrench until they cap screw/bolts were snug.
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Last edited by scooterforever; 04-19-2005 at 08:23 AM.
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