Originally Posted By: NHGUY
I'm surprised by now they haven't come up with a computer scenario for that...sit at a light for more than 30 seconds,and the computer will automatically shift the trans to neutral,step off the brake and it re engages the transmission to the gear range chosen on the shifter.
If it actually saved any fuel to do that, they would have done it. Heck, there are now a number of car models that SHUT OFF under those conditions and restart when you touch the gas! Bottom line, as others have said, modern torque convertors practically disengage at idle anyway, and so almost no additional fuel is burned (and almost no heat generated) from leaving the trans in gear. On an older car with a carb, big cam, fast lopey idle... yeah, it saves a lot of heat generation to drop it into neutral if stopped for more than half a minute. But not on anything remotely modern.