This does not work on newer OBD II cars.
In these cars, the ECU shuts off fuel flow when it detects a coast down condition, which helps economy. Shifting to neutral keeps the IAC open to alow enough fuel to idle the engine. However, all accessories are not driven at the speed necessary to keep everything working okay for the speed the vehicle is travelling, particularly the power steering pump (unless the steering is EPS).
For an automatic gearbox, shifting to neutral and then back to D at high speeds will causes further problems too.
I would NOT recommend this practice for OBD II ECU equipped cars.