I'm still new at this too.I used Finless Bob's video's to help set up my DX7. on my DX7 I checked my [ THRO HOLD ] it's set OFF ... Hold Pos. -5.0% ... SW: RUDD D/R for my Trex 450 SE V2 Looks just like the picture in the manual . When i set up my TX i don't remember messing with that. Is the flight mode set on (N) normal? Not stunt 1 or 2. That's the switch top left looking at the TX. Hold Rudder D/R switch should be on 0 that's the switch to the top right on TX . If it were on the TX would beep like crazy when turned back on with a warning. Check out Finless Bob's Video's setting up the DX7 on HeliFreak.com. Maybe the throttle curve is not set up right. You'll have to register to view the videos it's free to do that , that might help.
http://www.helifreak.com/showthread.php?t=41692
http://www.helifreak.com/showthread.php?t=28681
Rich