Your cat should still be ok. However, additives, race fuel and all that Octane Booster Horse Shit can coat your cat and lessen the ability to burn off hydrocarbons. I am not for additives. It you can't install it with tools it doesn't add power. With the exception of NOS. Anyways, I would go with a tune-up first. Your car could probably use it anyways. If that doesn't work, the cat may need to be swapped.