My '00 Civic (with knock sensor) is showing ~10% mileage improvement with a WAI pulling hot air from right next to the exhaust manifold. Aside from driving style, it has been the best single thing I've done for FE.
I recently got the idea to block the door from the exhaust manifold to the breather in the open position all the time to act as a WAI. Since doing this I've been seeing considerablely better mileage. MPG since doing this have been 46.478, 41.976, 44.198, 44.2 and 42.853. Some of these mileages are in line with what I usually get during summer months when the weather is warm and have summer blend gas.
Philip1 
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