Scion FRS Subaru BRZ Toyota 86 Resonator Plug

The Scion FRS, Subaru BRZ, and Toyota 86 have a resonator tube that runs from the intake to the firewall on the passenger side of the interior.  This sends reverberated engine noise to the cockpit and nothing else.  If you removed this tube, such as when using a cold-air intake, the hole must be plugged or water and debris can enter the interior.  Some kits come with a plug that requires removal of the original rubber gasket in the firewall.  That can be a pain to put back in if you want to revert back to stock for whatever reason.  This plug retains the grommet and uses it as a seal.

In order for this to work properly, simply pull out the resonator tube with the grey snorkel at the end from the engine side.  You can either leave it dangling there or remove the setup and cap the intake, or replace it with a cold-air intake which I recommend.  Leave the rubber grommet in the firewall and push this plug into the hole from the inside of the compartment on the passenger side.  That will create a watertight seal to keep out water, grime, and noise.