New Cats?

it's either cats, or more likely just your cat ECUs. I'd pull the ECUs and inspect for cracks.

 

What year is your car? How many miles? On the 1995 355 there are two cat temp ecu's. One is for slow down 1-4 (right side) and the other for 5-8 (left side). The cat temp ecu's can be swapped and then you see which bank lights up to confirm that is the problem.

 

It's probably a bad cat ecu, or bad thermocouple. Both are easy to change and can be done by yourself. The tricky parts is figuring out what is bad, especially since you have a 5.2, which has only one slow down light.

 

+1.

 

+1

+2

 

Although the ECU's are a common failure, cracked headers causing an excessively rich mixture which destroys cats fairly commonly on the F355 is always a very realistic possibility. If this is actually the issue the raw fuel can wash out the piston rings, and if the cat starts to break apart the engine will suck in the material and destroy cylinders. You want to do a very thourough and proper diagnosis before making a decision..IMO.