At idle, yes. On the over-run (closed throttle at higher engine speeds) no. Most systems completely shut off the fuelling until idle speed is resumed.I believe that the hypermiler in the above post is wrong on one point. When your throttle is "closed" there is still air getting into the engine, because some amount of power is required to overcome friction and all of this air moving about in the bottom half of the engine. To create power, this air needs to be mixed with fuel (a small amount) before it is ignited.