Greetings Edimilson:Do you have any joysticks or other controllers connected to your computer other than a keyboard and mouse? It sounds like something is centering the Y axis of controller/joystick #2.
If you don't have any controllers connected to your system, you might check out the key assignments and controller assignments, and the sensitivities settings. One of them may be causing the throttle to return to neutral.
Please let us know if any of these help.
Good luck!
Ben