I've been looking into buying a performance chip for my 2003 Toyota Corolla S in order to gain some HP and it says increase fuel economy as well. This would just be a pre-programmed chip that connects directly into your OBD2 port. I dont know if you have to leave it plugged in order for it to continue working or you just plug it in and let it do its thing and plug it back out? And do you guys know if its even worth my 250 bucks for it? will it actually give me 10-40 more hp or anything at all?