hi Steve, I have the same issue with my 08 classic. it was down right dangerous!. I cleaned every linkage and every spring; I reset all my perimeters in my map but the problem persisted.
I then decided to remove my idler stepper motor as shown in Warp 9.9 photos. I took the rubber boot off and soaked the motor in WD 40. I then pushed the "arm" in and out about a 100 times (exaggerated); replaced the rubber boot and put it back on my bike. I then reset my map tune and gave her a 12min tune. hey presto, bob's your uncle, all fixed! that was a year ago and no more problems. I think it was just gummed up with dirt and needed lubrication.
maybe this will work for you. total cost was about 1hr of time.
cheers