Sorry I didn't explain .
Disconnect the battery ground cable (at the battery, NOT the disconnect switch) for a minute or so..reconnect fully ...then..with all accesories off, start the engine, "without touching the throttle", and allow to idle all on it's own for approx. 10 minutes (while watching the gauges of course

).
This "resets" the Computers "Relearn", "Adaptive Logic" Idle Parameters. From this relearn input data the Computers will have adapted to any changes in system config, such as a different exhaust system.
HTH's
Regards, JRV