[jiggyboy]

The emission restrictions have become so strict over the years that there’s no longer enough carbon monoxide in the exhaust of a new car to kill you.

Let me go further. There's no longer enough carbon monoxide in the exhaust of many cars that have passed a smog test to kill you, not just the new ones. Per Wikipedia, 0.04% CO in the air can be fatal. A glance at the smog test on my 20-year-old beater shows that it generates less than 0.01% CO at idle. That's "slight headache within two to three hours" territory.

Let's see the toxicology report, and let's see that Hummer's smog test.

[Old Professer]

CO is almost perfectly matched in weight with air and immediately tends to go into flux; not only that but as the engine continues to run the result is a cumulative addition of harmful gases collecting. Now how easily could these gases enter the living quarters?