Slight sticking of throttle

I get a slight sticking of the throttle at times, coming off idle or when cruising. Seems like more when I've been on the road for awhile. Whenever I look at the throttle body under the hood it seems free and easy to move. Do these throttle bodies ever ice up after driving for awhile? I've already lubed the linkage inside the car and thought it was fixed, then later in the day when driving about 40 miles it started again.