Idle is adjusted like a car carby, there are a few things that can cause an idle hang up.
Sticky or frayed inner cable(not lubed)
Outer cable jammed or squished on frame parts or under tank.
Routing of cable not taking easiest route(cable too short)
Improper adjustment of cable free play.
Thumb throttle needing lube.
Worn nipples on end of cable moving when throttle closed.
Butterfly shaft sticking or return spring weak.
Loose screws holding adjuster plate(if it has one)
There's been a couple of threads lately with sticky throttles, check 'em out.
Sticky or frayed inner cable(not lubed)
Outer cable jammed or squished on frame parts or under tank.
Routing of cable not taking easiest route(cable too short)
Improper adjustment of cable free play.
Thumb throttle needing lube.
Worn nipples on end of cable moving when throttle closed.
Butterfly shaft sticking or return spring weak.
Loose screws holding adjuster plate(if it has one)
There's been a couple of threads lately with sticky throttles, check 'em out.