a sensor monitors intake air pressure and feeds this info to engine ecu.
normally it sees vacuum as engine sucks air in.
imagine the confusion caused by adding s/c or turbo.
ecu says... huh? wassup? +ve pressure... help... limp home....
the tte sub-ecu (black or silver) fiddles the signal so the engine ecu doesn't 'see' +ve pressure.
pretty much any add on turbo or s/c kit will have a similar gizmo.
any car... not just lexus.
hope that helps.
oh, ref my fingers,
they're just very stiff at the mo and reluctant to do as they're told :duh: