I had the same trouble on my '06 classic. Here's what worked for me.
Pulled the rear Throttle Positioning Sensor, put it up on my bench. It's a simple potentiometer. Set it face up (flat blade screwdriver type socket), spray some WD-40 into it, cycle the pot several times with a small flat blade, this cleans the wiper and circuit. Re install in the same position that you removed it.
Adjust the rotation for the best idle speed, one way kills it, the other high revs it.
Not that hard if you're mechanically inclined. I've been riding it just fine for a couple years now. I think it picks up grime from the road.
Don't be skeered, and don't fall for lousy mech's that advocate jacking up the radiator cap and parking a new bike under it.... new throttle body.... That guy needs to work at Crispy Creme!