It's mostly because the BS tends to not downshift at lower rpms and speeds, meaning whatever gear it is in, it's running at like 1200 rpm or so. Goose the gas to get it to shift into a lower gear, the rpms go up and the shudder goes away. I don't know for sure, but I don't think it uses 2 cyl mode at low speeds. I would think that would be for steady highway speeds. If you put it in sport mode, it will hold the rpms higher at a given speed and the shudder will be gone. It will be at the expense of gas mileage though. I notice that sometimes at stoplights there is a shudder. I don't know if it will go to 2 cyl mode when stopped or if it is because the 3 cyl is just rough at certain rpms.