Check engine soon light?

If the light is blinking on and off, that usually indicates some type of misfire, in which case the cat can be damaged with continuous driving, have it looked at. The SHO is known to require more then average maintenance. A friend of mine has a 1987 SHO, yamaha engine 5 speed, super mint w less then 30k on it, he's the original owner. Always futzing with it, it is a beautiful car though