Have you checked the fuel pump boot cover? (the rubber piece that covers the whole thing, has the 2 gas lines running out of it) that was my problem. Also, check the boot again. Just because there are no visible leaks doesn't mean that it's not leaking vapor. After time, they become dry rotted. The boot shouldn't have any cracks at all in it (you'll have to pull it out to see) and the cover should be soft and pliable, and sit tightly on top of the whole thing. If it's hard and brittle, there's your problem. Scott