Money Want to start your car to heat it up? Here’s why doing so in winter weather may be a bad idea. December 14, 2022 Coral Murphy Marcos, Dalvin Brown and Ben Tobin, USA TODAY Comments Off on Want to start your car to heat it up? Here’s why doing so in winter weather may be a bad idea. Letting a car idle requires more time for the vehicle to warm up and allows excess fuel to get into the engine, which isn't good for wear and tear.