What to do about check engine light that won't stay off? on 2000 Saturn LS1

My check engine light is flashing, I had a tune up and it went off for about 1 week, I had the catalytic converter replaced and it was off for about an hour. It is vibrating so bad it feels as if the engine is about to fall out.

Asked by for the 2000 Saturn LS1
get a shop to do a build up of the motor to see why it is missing.