sigfish

OK. I have had it with the mechanics in my town. I am unable to do much work on my vette due to physical problems and have had to rely on others, which isn't working out to my benefit. I had Midas install a Borla cat back and they put a bolt through the cat. They didn't tell me this and spot welded it. On a recent trip I noticed the engine idling rough and a noise under the car. On inspection I saw the hole and obviously the weld didn't hold. Upon confrontation over the issue, they said it was ok to weld the hole, confirmed that they did it and welded it again. It is still running rough and will die or sputter when at idle and I also notice it "lag" when driving, almost like it's missing, or a cylinder isn't firing. However, there are no codes or warning lights that appear, so my question is... Is it possible that the cat has been damaged to a point where this would be caused, and is it ok to weld a cat. It's a 1995 LT1 with 89000 miles. Thanks for your help.