Deleted the key assignment (Y) with no effect.
That's not what you should have done. Doing this, you deleted the Slew
main toggle event event from the KEYBOARD, so you cannot put the airplane in slew with the keyboard anymore.
You should have removed the Slew
movement event from the Axes of the JOYSTICK instead. And be sure that all Axes (in SLEW mode!!!) were removed from ALL joysticks.
If you don't want to do that, then you must calibrate ALL joysticks and set the Null zone correctly.