Aftermarket BOV install (HKS SSQV)
For this install, you'll need an STi and an HKS SSQV BOV, although these instructions apply to any aftermarket BOV kit designed to fit the 2002+ WRX (including STi).
Tools needed: socket set
1. Open hood.
2. The BOV is the piece attached to the intercooler. It should be fairly obvious and easy to find. Running to the BOV should be 2 hoses. One is small and if you have a boost gauge (factory or otherwise), you should be able to follow the line to the firewall hole. The other hose is large in diameter. Detach the small and large hose. If the large one really doesn't want to come off, save it for later.
3. If I remember correctly, all that is needed to remove the stock BOV now is to remove the bolts holding it to the intercooler. Remove the bolts and pull out the BOV. If you get to this point and had saved the larger hose for later, remove it now. The clamp holding it on will put up a fight but it can be done.
Your stock BOV should now be removed. Now it's time to install the new one.
4. With your HKS SSQV kit, you should have a 34mm aluminum plug. Put this plug in the larger hose you removed from the stock BOV (the recirculating hose). If you have a different BOV that recirculates air, there will be a place to attach this large hose to the BOV once more.
5. Take the new BOV and put it exactly where the stock one was, being sure to use the gasket that was already there. Put the stock bolts back in and tighten them some.
6. The smaller hose now needs to be attached to the new BOV. The place it attaches to looks exactly the same as it did on the stock BOV. The new BOV may have come with a small section of hose and an adapter to make it all fit, and if so, use them.
7. With your BOV securely on the intercooler, the large hose plugged and small hose hooked up, you only need to use the clamps provided and already there to make sure you don't blow any hose off while driving. If you think it is needed, use zipties.
Now you need to try starting up your car. If you have no problems, it should just start up like normal. If anything seems odd, check for leaks.