It makes sense to me. Like I said earlier I used to be a neutral stopper as well. Then I thought about it. The way I understand it, when you totally take your foot off the gas,the only thing keeping the engine running is momentum, not fuel. The way I thought about it was like when yourcar won't start and you have to pop the clutch to get it started. The momentum turns the engine over. When youpop into neutral, the car has to idle to keep the engine running, thus injecting fuel.
I would imagine most cars operate this way, but I could be wrong.

 

Not sure, but I think it's very common. Starting with mid-to-late '80s when there was enough computing power on-board to add stuff like that.

Just based oncars that I've owned...
'74 BMW 2002tii - you kidding?
'82 Rabbit (Bosch CIS)didn't have it.
'86 Jetta (Bosch CIS with more sophisticated control)probably didn't have it.
'89 Saab 900 (Bosch LH2.4)- YES.
'95 Integra GSR - YES.
'98 Accord F23 - YES.
'01 Saab 9³ (Saab/NGK Trionic-7) - YES.
'03 Accord K24 - YES.

I think my '05 Saabaru WRX continues to injectjust enough fuel to keep the first catalyst hot.

 

The biggest difference between a neutral coast slow down and just letting off the gas (besides a little economy) is that it can help your throw-out bearing a clutch last longer. Is it a huge difference? no, but neither is economy differences or anything like that

 

And JimBlake said, "When the rpm is substantially above idle (maybe 1300 or more?) and you completely close the throttle, the ECU willNOT firethe injectors at all. So that useszero fuel; less than idling."


But that would imply that the engine is running without fuel. How can that be? I'm not being argumenative, I just don't understand. Engines can't run on zero fuel, even if the wheels turning the tranny keep the engine spinning, can they?If it doesn't die/stall, wouldn't that imply that fuel is being burned?

Thanks for you time in educating the rest of us.

 

When a motor is idling it has to provide some sort of spark/power to keep the pistons moving and crank turning, when you are slowing down the moment of the car/tranny keep the engine turning over it just gradually slows down until it needs to supply fuel to continue/maintain the momentum so it doesn't require combustion to maintain it at that time, since the only thing combustion does is supply energy to keep the crank turning when you coast/slow down in gear it simply uses the exsiting energy to maintain itself.... make more sense? Clear as mud?

 

I'll give it a try but not convinced that mileage will improve by coasting in gear(clutch out) with throttle closed over coasting in neutral with throttle closed unless you do a lot of coasting.

 

The difference is minimal unless, as you stated, you start coasting from a ways back, if I see a red light a ways up I will drop it into neutral and slowly coast to a stop to save my brakes more than saving my fuel... As far as I'm concerned fuel costs a whole lot less than a new clutch, throw-out bearing or brakes so I'm a coaster and I will coast as soon as I see a red light, when it turns green I go back into gear and slowly acclerate to match traffic that way I don't use my brakes unless I have to

 

are you one of those guys who will coast a mile out? or do you get within a reasonable distance before you do that....

 

Heck no... I'm one of those super annoying people that will coast from a block away *L* not a mile out but yes, as long as there isn't a ton of traffic behind me I will coast from a ways out, I just make sure to gauge it so that when the light turns green I'm on the bumper of the car in front of me before he goes through the light so it doesn't hold up traffic

 

Maybe it's a question of semantics. You could say during coast-down that the engine is NOT running. Meaning it's not injecting gas, and there's no combustion.

The engine is being turned externally by the momentum of the car or the slope of the hill you're coasting down. I imagine that if you're in the mountains and you can find a 6-mile downhill, the enginewould actually cool down.

The trick here is that as the engine continues to slow down & goes below some particular speed (I guessed 1300), the ECU starts injecting fuel again. At that point point you can sometimes feel a little shudder as it starts. If the ECU was unable to do this instantly, the engine WOULD stall. Restarting smoothly is the reason it switches at 1300 instead of right at idle.