I have a 95 Mitsubishi 3000GT has a rough idle and missing when accelerating

What is your question?

To describe the sounds it's kind of a sputtering rumbling sound and lacks power and acceleration like it's running on 3 cylinders but as soon as you get off the gas or downshift it sounds fine

How long has your 1995 Mitsubishi 3000GT had this problem?

a few days