After driving for about 10 minutes in my 87 gt, If I come to a light or somewhere where I am stopped for a few seconds, I notice my RPMS jump up and down and the car feels like it wants to move a bit, it sounds like its breathing heavy because you can hear the exhaust as it does it, and you can even hear the cats because it sounds like they have marbles in them, its a "clinky clanky" kind of sound as the exhaust passes through them, but more importantly whats causing the rpms to slowly jump up and down