Maybe check your control mappings, to make sure you have nothing else mapped to any of the throttle commands.
That behaviour does sound like it might be something to do with one of your controls being mapped to one of the ‘throttle(0-100%)’ axes, but still worth checking for other unwanted mappings to any of the throttle commands.
Same here. So far this A320 Fenix has been a waste of money. Throttle just surges out of control. No other aircraft has an issue. No answers for this anywhere. I give. 12 months later, I know…
I found the issue: throttle axis has to be set to axis 1 and axis 2 for each throttle. I had both set to one setting which was the wrong one. It works in PMDG but not Fenix. Also had to set reversers to zero/zero so I have none I think. I want my idle to be all the way back. I think it wants you to leave an inch at the bottom for reverser and that doesnt work for me. I have a Thrustmaster X56.
Did you do the throttle calibration inside the airplane, through a menu in the MCDU?
There are a few YouTube videos how to set it up. I think there are also some instructions in the FAQ on the product website. It takes ~30 minutes to set up. Nothing compared to the time you need to learn how to actually operate it properly.