this car is on gas conversion and whenever its switched over to gas it will just vibrate and it feels like its going to stall...even on petrol the engine runs rough under acceleration in park or neutral.......me and my dad were under the car and i told my old man to sus out the cat because it lets off a rattle everytime throtle is applied.....the cat is making a rattly pinging noise so i was wondering if the cat would casuse the car to behave like this?