The AIV warms up the cat? The AIV, afaik, does not warm up the cat. It introduces air into the exhaust stream to help the cat convert co to co2. It does so (at least on my car), when the throttle snaps shut b/c when this happens, the car runs rich b/c of port wall wetting. This was later fixed on the low port models of my engine by places teh injectors closer to the intake valves and increases intake air velocity.