On my 91 / 92 Jettas there was a thermal valve on the side of the airbox which would draw warm air from behind the engine when it was very cold out. If it's below freezing I would leave them off, or redirect them to the front corner of the engine bay so they get cool but not freezing air.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.