What tuner wants to offer a burble / popcorn tune option? We can use my car for testing since everyone else is a whiny bitch about some pops and crackles now that we have the ability to switch maps on the fly. DM me.
On deceleration, when we want to enable this "feature", the tuner in effect must introduce unburned gasoline and air into the turbine or catalytic converter so it ignites, creating the condition. It can be achieved by keeping the throttle open while disabling the spark event while allowing a low duty-cycle injection event.
Unburned fuel accompanied by air leaving the exhaust port creates a lean condition causing detonation in the turbine or catalytic converter. Since it only happens for a very short time, in those ecus where this is possible, it's probably not too big a deal in terms of cylinder wear, but think of the amount of experimentation required to achieve the proper results. Easy to create too much fuel, bye bye cats, extra cylinder wear and possible turbine blade damage.