The car doesn't want to stay on idle coming towards a stop. So you're coming to a stop sign, it's in 4th gear. Put it to neutral and the car won't go back to idle, instead it will come close to dying or have a hard time idling. You will have to give it some gas to get it back to idle (780-800 rpms) My guess is that it's possibly a boost leak OR the throttle positioning sensor having low voltage.