GpZ 1100 throttle problem

Hello! My Gpz 1100 won't lover the rpm when revving like it's having vacuum leak somewhere but I checked inlets and they are fine. It happens when engine is cold, but it's more prominent when engine iz warm, after longer drive. When I rev it to 4k and i let the throttle, it stays on 4k like throttle cable is stuck but it isn't. So, my question is what could be problem, what to check? Thanky you