You're more likely to survive now, but it's definitely nowhere near an impossibility. There are tons of stories in the news on a regular basis of people who left their cars running accidentally and died of CO poisoning, mostly elderly who likely didn't realize they left it running.

https://www.nytimes.com/2018/05/13/business/deadly-convenien...

Also, catalytic converters don't actually work until they're at operating temperatures.

https://www.abe.iastate.edu/extension-and-outreach/carbon-mo...

Why is that?