almost every chevy, early 90s and older, has a diverter door in the snorkel coming off the large circular air filter housing over the engine. typically (and what's in my truck) it's set up with a thermo-mechanical vacuum switch and a vacuum servo operating the door to pull air either from a CAI to the fender or from a tube going to a heat-shield around the manifold. in my truck it tries to maintain about 100-130f intake temp. if it's too cold, the switch opens the vacuum line to the servo moving the door to block off the CAI and open up the WAI from the manifold. could use something like that but with an electromechanical vacuum switch.
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-Russell
1991 Toyota Pickup 22R-E 2.4 I4/5 speed
1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
mechanic, carpenter, stagehand, rigger, and know-it-all smartass
"You don't get to judge me for how I fix what you break"
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