This site is being deprecated.
Please see the official X‑Plane Support page for help.
Please double check your equipment set up in the Joystick & Equipment menu and make sure the throttle axis is calibrated (bar will be green) and set to the right thing in the drop down. If that doesn't work, you can try moving the preferences folder to the desktop to reset to defaults in case something got accidentally mixed up.
If none of that works and this is a new development (if the behavior changed when you updated X-Plane for example), you can file a bug report here with specific steps to reproduce the issue.
This site is no longer being actively maintained.