2004 yaris hatch, 2nz-fe, DFCO in all gears?

[Yaris Hilton]

Originally Posted by scape

I'm so confused by that...do you mean when the engine and transmission are not engaged?

No. I mean when the engine and transmission ARE engaged. The coasting car spins the engine faster than idle speed. When an engine's just getting idle fuel and being spun faster this way, the fuel burns incompletely and hydrocarbon emissions go up.

As for the fuel economy effects of DFCO, it will vary depending on your circumstances. Going down a moderately steep hill, it will help to slow the car and it will save whatever fuel the engine would have consumed at idle power. The brakes will have to be used less. Anytime you're coasting to an eventual stop, cutting off the fuel will save the fuel that would've been burned during that coast at idle power. Not much, but every bit adds up. If you're doing something like pulse and glide in gear on level ground, the car will slow faster with DFCO, and you'll have to get back on the gas for a pulse sooner. You'll likely burn more than you would coasting in gear at idle power or in neutral or with the clutch disengaged with the engine idling. But I doubt that most people will really notice the difference under most circumstances.