apparently after I changed the tx setting to pcm, the throttle hold doesnt seem to work. Any ideas on why, or how to fix it?

i'm using the old T6XH(s) from futaba (which supports pcm) and a pcm reciever also from futaba R146iP... on a zoom 400 (belt) with Align 20A BEC... everything else works fine, its just the throttle hold! =/ haha quite mysterious...