Exhaust sputter

Water is one of the byproducts of your cat. I'm not sure why some systems produce more water than others, but all of them do produce a small amount of water. I had a Jeep that produced massive amounts of water. With the old Jeep, there was a return tube on the cat that fed back into the intake. There was so much water dumping back into the intake, it actually would ice up the carb. I finally disconnected the tube, and ran it that way in the winter. Usually every fall, I would forget and get pulled over to the side of the road when it quite running. Just a matter of pulling the tube, and then knocking the ice down into the engine where it would melt, so I could start it up and drive it. Strangest thing. I never did figure out why it did that, but just dealt with it. I don't think it was a head gasket, as it never used water.