I was having all sorts of problems with flying choppers using my CH setup (pro throttle, fighter stick and pedals). Just couldn't get the collective to be sensitive enough leading to ping-ponging flight and lots of crashes. Controlling the collective with Q and Z keys was fine however.
Then I realised when I was configuring the controls in-game that BOTH the Z-axis and slider where highlighted. When I unmapped the slider (on my fighter stick), the throttle now works perfectly. I can now fly choppers as intended and with precision.
Although the slider was not set in keymapping, it must have been conflicting in some way with the Z axis.
Just a tip I thought I'd share in case you're having similar issues. Happy flying.