CO and CO2 produced by the engine is going to come out of the exhaust at the back. Your AC will take in air from the front of the car. In a parking lot or other well ventilated areas, I don't see a big cause for concern.

Also modern cars produce orders of magnitude less emissions its actually somewhat difficult to kill yourself with one now, you essentially have to run a hose from the tailpipe to the cabin.

You still have an engine that is producing a certain amount of power, and this is associated with a minimum rate of production of CO2. Some of the other interesting emissions are greatly reduced in modern engines, but the CO2 production hasn't fallen that much.

I was just going off what I heard from a EMT to be honest, he said those types of suicides were much more successful early in his career.