A throttle body spacer bolts on in between the intake plenum and the throttle body on the engine. I believe that the idea is to allow the air+fuel to mix more completely and provide better combustion. I have one on my taco...I have also done the deckplate mod, and installed a k&n air filter...the throttle response is very good. I don't think I gained much hp or torque but the response is very quick and with the deckplate mod the engine definetly sounds a litte more mean.