When im going down the road, every once in a while i'll let off the gas the rpms stay up and I have to shut it off and restart it and they still stay up and i have to restart it a couple time to get it back to normal. The throttle moves smooth and returns smooth. It seems to happen when im about 1/4-1/2 throttle and cruise and then let off that the rpms stay up and wont go down. Any help???