Idle Check

There is no fix as it is not broken. It is doing exactly what it is designed to do. The only way for it to advance to stage 4 is to stop and let it do its thing. The one thing you could do is try and take a longer route until you get to the downhill. Another thing you could try is if you are stopped at a light or in traffic prior to the hill is put your left foot on the brake pedal and press the go pedal with your right foot until the engine comes on. If it is ready to go to stage 4, it will stay on and do the idle check.

If it is any consolation, it is only using 1.2 L/100 km which is next to nothing. On your display, it would be showing 99.9 MPG because it can't show the real value of 235 MPG (Imp) (196 MPG (US)).