If you find that your car is running poorly during the winter months it could well be small amounts of water in your fuel. These small amounts of water freeze and cause your car to run badly.
Most gas/petrol that we buy does have some kind of gas line antifreeze that prevents the water from freezing. However you can buy a product called 'dry gas' that will help to remove the water from your vehicles gas tank. Ask at your local motor accessory shop.
In good old TipKing style I do have a money saver. You can use rubbing alcohol that contains 99.9% isopropyl alcohol, which costs about a third of the price of commercial dry gas. Do be aware though that some brands of rubbing alcohol do contain 70% isopropyl alcohol and the rest is water. So do not use that as it will defeat the object.