It sounds like high vacuum at idle or deceleration is cocking the secondary throttle blades and causing them to bind in the bores. I would ask Holy to replace the throttle body.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy