Money How often should I start my car and let it idle in cold weather? Answer: Don’t. December 16, 2020December 16, 2020 Coral Murphy, Dalvin Brown and Ben Tobin, USA TODAY Comments Off on How often should I start my car and let it idle in cold weather? Answer: Don’t. 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.