I have an exhaust leak under my car. Will idling in my car kill me?

[Kramer]

How long would it take? What are the downsides?

 

[UpandDownPrincess]

It depends a bit on your car and/or country, but no.

Cars today and for the last several decades are made with an emission reduction system that reduces the amount of CO produced.

You would likely run out of gas before you die.

 

[signifying nothing]

Yeah, you need to get the CO levels as high as possible, as fast as possible to minimise the intermediate symptoms of poisoning (headache, confusion, nausea, vomiting).

You might consider a small gasoline powered engine. And I think these fatalities show how easily you can die from CO in the right circumstances.