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The Modfather
2019 Impreza 5dr Sport - Manual
8,091 Posts
Discussion Starter · #1 · (Edited)
My 2004 Forester has a little over 100K miles now. I've been experiencing some boost issues. More about that here:

However, in my quest to find the issue I discovered that the diaphragm in my recirculation valve (AKA BOV) was leaking vacuum. For me it was a gradual thing. It did not seem to have any effect on my vacuum as my readings seemed fine. I have both a digital and analog gauge.

If you have a high mileage turbocharged Forester (or other Scooby maybe) it may be worth your while to check if yours is leaking too.

It's a pretty simple matter, just remove the line small vac line leading to the top disk on the valve and pull a vacuum on it. Pulling a vac can be as low tec as attaching another hose (something like a windshield washer hose) and sucking on it with your mouth like a straw. You will be able to draw a little bit of a vac but if you can continually pull air in, you have a leak. If you have a mighty-vac you can use that too. I was too lazy to look for mine.

Swapping out the recirc valve is not that hard, you need to move the large hose clamp back on the return line and then remove the two 12mm nuts holding it on. The lower nut may be a bugger to get to if you don't have the proper tools. If that's the case you can just remove the IC and do it that way:

On another forum someone mentioned that even though they have the same MY Forester they have less miles (a lot less) so they will check in the future. Upon further consideration, age may have bearing on this issue too not just miles. In fact a car that sits may even be more prone to problems. The material in question here is some sort of rubberized fabric. Sitting still may let it harden more quickly, not flexing for some time. In my experience, machines like to be run and the longer they sit the more issues you have. I did notice that the diaphragm's damage was all at the bottom 180° area. The part that faces down. I suspect the oil vapors are what attacked the material. The thing is I have a catch can and my IC was for the most part pretty clean, if you remove your IC and have a fair amount of oil (not uncommon) I'd be very suspicious of the bypass valve leaking


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