I got bored at a long red light the other day and I started playing with the shifter, putting in in various gears. When I put it in neutral, I noticed that the vibrations from the engine were noticeably decreased. It occurred to me that this might save fuel, because the engine isn't working against the transmission. Would this work, or is my logic faulty?

 

Weeeeell, I don't think it works exactly like that. Although, I can't recall the exact reasons why (sorry), neutral won't save you gas. You drive an automatic right? Your car is basically at idle anyway when it's stopped (torque converter doing its job). Furthermore there throttle is 'closed' already, so there's no reason to add extra fuel... See what I'm getting at? Your car isn't gonna go below the a/f parameters for idle, so it just won't save gas.