[Climber76]

Sorry guys, I disagree. On a mild downgrade in my automatic Tacoma, once it has locked the torque converter (which it does quickly) in fifth at say 40 MPH, if I lift of the gas completely the truck slows immediately. If I pop it into neutral (as I would with a manual) it rolls and maintains speed. There is mild engine braking with the auto any time you lift the gas, just as there would be with the manual. But with the manual it's harmless to go in and out of neutral. I'm less sure that's benign for an automatic. Any transmission techs out there with an opinion about whether it's harmful to go in and out of neutral with an automatic?

I've had a chance to test this issue extensively with two matched Honda Civics, one manual, one automatic. The Civic automatic also does a good job of locking the torque converter under light loads -- usually a good thing. But it does kill the coasting. We got 32 mpg consistently with the manual, and are getting 28 in the same conditions with the automatic. Pretty disappointing. I would expect similar results with the Tacoma.

Per the comment earlier that the fuel injection system closes off all fuel flow when the throttle is closed, I don't know whether that's correct or not. Seems unlikely it would go below idle flows. IN any case, my point was the engine braking effect, which is more significant since you have to then apply throttle to regain speed you lose from engine braking.

The other thing that kills fuel economy with automatics is the compensated idle: fuel flow at idle is boosted slightly to compensate for the load from the torque converter. So manuals burn a bit less sitting at a stop light. All this little stuff adds up.

Again, my experience with this stuff may be unique to the city I drive in, where there's lots of free transportation to be had on the way back down the hill...

Re the question about my display name, it means I like to climb stuff and I'm old as dirt