All those wild claims in the e-bay add is not sending your BS meter off scale? Come on now. The "theory" that modern EFI cars are running rich all the time is just plain WRONG. They would never pass smog if that were the case. All modern engines are set from the factory to run lean-of-peak except at startup and full throttle. A "chip" can be just as phony as fuel line magnets and other devices that have come along every time gas prices go up.