HAD INTAKE GASKET PROBLEM AND CATALYTIC CONVERTER PROBLEM, FIXED BOTH,

You need to have the codes stored i the computer of your car retrieved using a scan tool. Once you have the code/s they will identify where the problem is likely to be or where at least to begin diagnosing the problem. If you have the codes please post them and we may be able to help. (The codes will be in the format P0420, P1566 ...)

Most likely it is a bad Oxygen Sensor located at the Cat Converter. And, most likely the repair facility destroyed it when they cut off your converter with a torch.