When I turn off my 2001 Galant, it sputters for a second, does anyone know why?

shut it off in gear...after it stops switch to park and take out your key~...this phenomenon is called "dieseling" the fuel supply should be cut off immediately and should not be any fuel there to keep it running~ perhaps your fuel pressure regulator is not working properly and allowing TOO much fuel through....inspect this one~

dieseling can be caused from a "hot" engine condition...this may be caused by a vacuum leak, incorrect combustion...the EGR should engage if the operating temperature gets to be so much...check the operation of your EGR valve~