95 Range Rover runs rough and shudders when accelerating

#1

This rig sat for about 6 months without being driven or preservative added to the gas. Now the gas mileage is abysmal, it runs rough and when you accelerate it has no ‘get up and go’ and just kind of shudders. My bad for letting it sit, but what is the fix?

#2

It could be bad gas causing this. Use up the old gas. Get a can of SeaFoam Engine Treatment, and pour this into the gas tank before refilling the tank.

Tester