If you are going to "block the (heated air) hole" as some are suggesting, make sure you modify the airbox flapper valve so it is locked in the position where it covers the hot air inlet, thereby fully opening the cold air one. You can use a nail cut to the right length to replace the little thermostat device to do this. If you merely remove the tubing and plug the hot inlet, the flapper valve will block the cold air inlet and you then have both inlets blocked, choking the engine.

The intake air preheat function is designed to reduce exhaust emissions in cold weather by enhancing fuel vaporization. It does not speed up engine warmup in any significant way. Its usefulness is questionable in a place that does not get really cold days, and does run the risk of frying your expensive Air Mass Meter, if it fails - which they are known to do.
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Bob: son's 81-GL, dtr's '94-940, my 83-DL, 89-745(V8) and 98-S90. Also 77-MGB and some old motorcycles.