Well, it usually interfere with the engine breathing. The sign would show up as bad idle or if completely blocked, then engine would stall.Not sure how much it costs because I usually do it myself. Takes 20 minutes, shop towel, and can of carb cleaner. I would hate to go to mechanic for this things because even if they work for 10 minutes, they would charge for 1 hour of labor. So I would think you would end up paying about $100 or so.