For those worried about disconnecting the pre-heat hose because of emissions inspections, a simple fix is to screw the flap inside the bottom of the air box shut so warm air from a hot manifold is permanently blocked. Removing the thermostatic plunger is optional. It's difficult to imagine an inspector noticing your handiwork.

The general consensus here years ago was that the pre-heat hose makes no appreciable difference in engine operation or how quickly it reaches normal operating temperature. Unless you live in sub-freezing Arctic conditions where a warm engine might spend a considerable amount of time with the air flap kept wide open, it's hard to imagine a noticeable effect on fuel efficiency. The cost of needing to replace the air box thermostat periodically as a preventive measure, and the risk of frying an expensive AMM and stranding you somewhere away from home if you don't, are pursuave arguments for disabling the preheat function.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now