No, you do not have to leave the COBB Accessport plugged in. The Accessport is a tuning device that allows you to reprogram the engine control unit (ECU) in your vehicle. Once you have flashed the new tune onto your ECU, you can unplug the Accessport and store it in a safe place. However, you can also use the Accessport as a monitor and data-logging device. For those functions, the COBB Accessport will need to be plugged in.