When your intake system is under boost and you let off the throttle, closing the throttle plate, a pressure wave builds and heads back towards the turbo intake turbine. This can be very damaging to your turbo if it is present for an extended period of time. To relieve this you have a Blow-Off-Valve, called Auxiliary Air Valve by Toyota, that opens when the system is under vacuum, the throttle plate is closed. This vents the air back into the accordion hose relieving the back pressure.

To test if yours works take your BOV and see if you can blow through it. If you can it is, like mine was, toast and is leaking your boost. You can buy the one from Toyota but those are expensive. There are two other options that I know of which are to use the BOV from a SAAB or Porsche and are $25-$30. There is a SOGI tip on installing them, as well as this one. I find mine easier because you don't need a lot of custom adapters.
Tools: Pliers
  Utility knife or hose cutters

Materials: Porsche Air Cut Off Valve(993.110.337.50)
  2 Hose clamps to fit your 1" ID hose
  Small section of straight 1"ID hose
  Flared bypass-hose from Kragen (B70773)
  Flat head screwdriver
  21cm of 6.0mm vacuum hose
  1/8" x 11/64" Vacuum Elbow (VACU-TITE 47410)
  1 Hose clamp for 6mm vacuum hose


Tear down
1. Disconnect the BOV vacuum line from the chrome pipe on the engine.
2. With the pliers move the hose clamps on the two air hoses on the BOV.
3. Remove the BOV hoses from the 3000 pipe and the accordion pipe they may be frozen on so try twisting or if all else fails cut them off.


While you are here
1. There is nothing really to look at when doing this upgrade as it is one of the easier ones where you don't have to tear lots apart to do.


Assembly
1. Cut hose sections. Cut the straight section of 1"ID hose 3cm long so it will fit perfectly over the bottom section of the BOV so it just matches flush with the bottom section. Cut the flared heater hose section at the point that is 16cm from the flared edge measuring along the outside of the bend.
2. BOV Place the two hose sections on the Porsche BOV.
3. Assembled BOV setup Place the two hose clamps on the BOV hose sections loosely tightening them down.
4 Now the vacuum elbow will just loosely fit inside the 6mm vacuum tubing. But because of the short length and how rigid the tubing is we shouldn't have to worry about it blowing off. But if it blows off that is BAD so I used a small hose clamp. The picture at the top shows what it is like put together.


Reinstall
1. Place the longer section of hose on the 3000 pipe.
2. Push the lower section of the BOV over the according hose connection. It will just make a good seal. It isn't on the accordion hose super tight but this side does not require a connection that is very tight. Mine was also held down by the hose above giving some support.
3. Tighten the hose clamps on the wider hose with the flat head screwdriver.
4. Use the pliers to place the hose clamp on the 3000 Pipe connection.
5. Place the 6mm opening of the vacuum hose on the chrome connection next to the 3000 pipe. Then place the other end on the BOV. The hose connection at the BOV side is a bit loose so tuck the hose clamp on the BOV end in the BOV "moat" so it will keep it from popping off.