I have a 2012 GTI. About a year ago i took off the stock exhaust and put on the eurojet turbo back exhaust without a cat. Now the car started to sputter when I accelerate. The sputtering is getting worse and worse. I took it to VW and they said its because there is no cat, the 02 sensor went bad and now the car is just dumping gas into the engine and not burning it off. Has this happened to anyone else? how do i fix it?