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I was wondering this because i have an auto and whenever I'm coasting the transmission is still engaged so the engine is reving 1500's.
But when i switch it to neutral RPM drop to 600, therefore it will use less fuel. Plus in neutral i can coast for a longer distance.

The only concern i have is that this will weaken my transmission.

 
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i dont no what it will do to your tranny, i have a manual transmission and when i aproach hills (downhill) i always put it in neutral, it does improve mpg so it would be the same for yours, im not so sure about an automatic tranny going in and out of neutral though...

 
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Actually, you're better off coasting in gear. I can't remember the stuff off the top of my head, but it takes more gas to keep the car running in neutral.

 
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Mike your reasoning is flawed and will cause premature break wear on the car. The tps position is at 0 when you release the gas pedal rpms are not a good means of judging gas usage when coming to a stop, if the tps is at 0 then the car puts in no more gas than when its idling, the rpms raise is just the cars trans downshifting to assist in stopping, its not using more gas to do that. 16 years of working on cars and learning the ins and outs of how they work has taught me that.

 
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Fuel injection, that is. When coasting it will not be injecting more fuel, rather less.

 
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Alright guys, thanks for clearing that out for me.
I used to do it but always had a bad feeling about it lol.

 
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more fuel used in neutral than in drive, and its always a bad idea to force the trans into gear (or neutral) while the car is moving.