I believe it is a self check loop, and lets not forget we don't have a throttle cable so it doesn't have to cut timing it just gives you less air via the throttle plate, it could also limit cam advance,
it is not just a scion or toyota issue I assume this will be the new standard.
http://www.motoiq.com/magazine_artic...ir-intake.aspx
MotoIQ article talks about the technology a bit, I thought they had a better description than what i found in this article, a search for ETI on their site may provide more depth, My above description is just a general shot from the hip attempt to outline the issue that required correction.