[tholyoak]

P1502
The position of the throttle is controlled by a digital position controller which emits a pulse-width-modulated (PWM)duty cycle and a direction bit.
After the output stage has been deactivated, the throttle is brought into emergency air position by means of two springs. This return of the throttle must take place within a certain time. If this time is exceeded, a fault is stored in the memory.

You can try and clean any varnish and gum buildup in the TB and see if that is restricting the return of the butterfly to the closed position. If not you need to replace the TB.

Todd