Is your vehicle burning oil in any of the cylinders, as that would be the only reason you would have the anti-foulers on there in the first place!
The most obvious thing is the anti fouling attachment. If yours is the PT Cruiser it is a modern engine and shouldn't need them, as it will set a code when there is an issue. Most likely your plugs are running to hot and or earthing out. Take off the anti fouling device and see what happens.
General rule of thumb is, if it smokes on start up, or when you plant your foot on the accelerator then it is usually valve stem seals. Basically not very expensive.
If it smokes on start up and while running, generally worn rings and gets expensive.
Black smoke: Fuel
Blue smoke: Oil
White smoke: either blown head gasket or extreme damage.