Boost gauge, turbo cough

[Nilao]

870 turbos are air controlled. The one I had loved to chuff. It was the air cylinder binding up and then releasing once enough air pressure was applied to make it move too far. The ecm saw the backpressure skyrocket once the actuator freed up and dumped the air pressure all at once making it chuff from the sudden release of pressure. Could be your issue as well.