Estimated range of miles on my car go up and down in seconds?

I have a 2009 Altima 2.5 and one minute it says I have 30 miles left to drive and another second it says 14 miles left then it goes to 21 all in seconds. Can someone explain to me what's wrong with my car? I'm sure this car isn't supposed to waste that much gas, unfortunately it feels like I'm Illinois up the tank for a Ford Expidition instead.

That is a computer calculated number, it's using how your driving at that moment to tell you how long you have before you will run out (but it's always more). So if you are going up a hill you will be heavier on the gas than going downhill, so the number will go down.

Bottom line - those are not at all accurate, stop looking at it. I don't think there's anything wrong with your car, that is just not great technology. When you get below 1/4 tank, fill it up, then you never have to worry. You should not run it right to the end anyway.

Mine does that in my Mazda and it is based on your current throttle position/gear and the current fuel economy you're getting at that exact moment. So if you're accelerating then it's going to be lower

You're not too familiar with how the gas tank gauge sending unit works are you? Just like when you park on a hill instead of on a level surface and the gas in the tank moves around the fuel gauge can read differently. It's not wasting gas, it's just computing what the sending unit is giving it to work with and that changes as the gas in the tank moves around while driving!

Sounds like the TPS has an issue and the MAF sensor also I would change, there's other things involved, but those impact mpg and the computer the most.