This article is from the Toyota Tundra FAQ, by Steve Yee with numerous contributions by others.
A Throttle Body Spacer is an add on to your air/fuel intake area. Originally
used in the days of vehicles with carburetors, a throttle body spacer would
allow additional fuel/air mix to be present to allow for additional power, or
was used to "disturb" the air in such a way so that the fuel would form smaller
droplets. In current fuel injected vehicles, the spacer would allow for a
greater amount of air contained within the throttle body assembly so that the
engine would not have to work as hard in getting the air into the engine.
Poweraid currently makes a throttle body spacer for the Tundra. You can
contact them at www.poweraid.com . There is a clone of the PowerAid throttle
body spacer called the Helix Power Tower made by a company called "Street and
Performance Electronics". Street and Performance Electronics does not have a
web site, but you can do a search for the phrase "Helix Power Tower" in any
internet search engine.