I was wondering the same thing.

 

If the engine doesn't inject fuel, not even a little bit, at zero throttle, how can the engine itself run/burn? If you leave your car on for a few hours, wouldn't it run out of fuel? Doesn't it need fuel for combustion when it's on?

 

Read the second line of my statement:

"Take your foot off the gas while the car is in gear and not at or below idle and the engine does not inject fuel. "

 

It is still undergoing compression. Air is still entering the chamber and being compressed, but there is no fuel injected (and thereforce no burn thus the power stroke becomes just a stroke).

Notice how different your engine sounds when you lift off. No power strokes. Also, you have a different fluid medium exiting the engine with a totally different temperature. Without injected fuel, you just have air. Without combustion, you have relatively cold air. Different harmonics will accompany this different fluid medium.

Just because your engine is making noise, it doesnt mean it is undergoing combustion. Try reving your engine and then quickly take the key out at about 5,000 RPM. It should sound very very similar to just taking your foot off the pedal with the ignition still on. Untill it reaches idle and catches itself of course...

 

I understand what you are saying now slimjim. I just re-read your initial comment.

 

Just an optical illusion from the camera angle.