I just found that same thing on the drivers side floor mat. 13 month old 4Runner ltd.
It's where your flux capacitor plugs in
This rubber bushing piece fits inside one of the springs attached to the pedal. I found the same piece on the floor board years ago then looked under the dash of another 4runner until I found it.
Yes, pic please. Found the same thing a year ago.would you mind taking a pic of where it goes?
Guy said it fits a spring on the brake pedal somewhere. Several of us asking for a pic of where/how it fits. Awaiting said pic.Looks like a firewall plug of some sort.