[citation needed] But until you find one, let's do some math: Let's only look at CO2 and disregard the even nastier NO gasses emitted by a gasoline engine. EP

[citation needed] But until you find one, let's do some math: Let's only look at CO2 and disregard the even nastier NO gasses emitted by a gasoline engine. EPA data suggests a car produces 2,345 grams CO2 for every liter gas. And a modern, but without shut-at-stop, idling car burns about 0.75 l/hour. So 1758 g/hour CO2 for an idling car in your garage, which is roughly 63 m^3, and CO2 is 44.01 g/mol, so after an hour idling in a closed garage, you'd have 14,440 PPM CO2. That is enough to cause drowsiness in most, and some illness in sensitive populations. The OHSA standard for allowed exposure is 5,000ppm averaged over 8-hour workday.