Exhaust popping (DFCO)
Many people have heard the popping in their exhaust when you let off the gas, or push in the clutch.
This is caused by a safe lean condition that is induced under deceleration.
When you let off the gas, or push in the clutch the computer lowers the injectors to a preset limit (essentially turning them off) to save on fuel consumption. The spark timing is also pulled way back. This causes pops in the exhaust.
Many tuners simply turn this feature off with little regard to fuel mileage. On many vehicles, it is possible to still retain DFCO (deceleration fuel cut-off) and reduce the popping to a reasonable level, or hopefully completely eliminate it. Now the combo has the biggest effect on how DFCO works, and whether the sound can be tuned out while remaining active.
But this is just another good bit of info for the customer.