Originally Posted by dbenney
You will always get better avg mpg coasting in N vs D or S... this is due to RPM. Coasting in N is like putting the clutch in on a manual trans. As soon as you put it into N your RPM drops to idle, where as if you leave it in D or S your RPM is matched per gear and vehicle speed programming. as you slow down the auto will downshift raising the RPM... the higher the RPM the lower the MPG and vice versa.
I think the OP wanted to test the effectiveness of fuel cut-off during deceleration. This is why it's strange that the fuel consumption was higher in gear. If the fuel is cut off (regardless of engine RPM), it should burn NO fuel - vs. engine at idle speed in N. Anyone know what's goin' on? ...