Originally Posted by
Vadim Costing in neutral is actually bad for your gas. If you coast in gear (aka engine breaking), but stay in high enough gear your injectors will shut off. While your coasting in neutral injectors must stay on to keep the engine running.
Here's what I never got. If you are sitting in your driveway holding at 3K rpm, and take your foot off the gas, the car idles. Air is cut down to idle air, the MAF reacts to that, injectors supply idle amout of gas to match idle air for an idle mixture, and the engine revs down until it reaches idle RPM. So if you do the same while driving, whether in gear or not, why would it be any different?
The injectors are supplying enough fuel for idle as the air supply with your foot off the gas is for idle. It doesn't care how fast you're going, doesn't care if your clutch is in or not, it's just going to supply gas to match the incoming air. It simply engine brakes until you get to idle RPM since that's all the power it's making at that throttle location.
The only true way to conserve is to turn off the ignition when coming to a stop. Nobody's going to do that.