with the car on. it started to shutter or stumble. it has happened to me twice and when it does this i quickly turn the car off. why does it do this, and is it normal?

 

It sounds like you are filling up with the engine running which is a no-no. With the engine running and you take the gas cap off, you loose pressure in the tank. Always stop the engine when you are filling up. You're lucky you don't throw a cel.

 

giddeyup, what he said...shut her down, then fillerup