Had '99 Vette in to the Chevy dealer for oil change/transmission flush/anti-freeze flush/change. Was told by technician that I also needed an air/fuel induction service for $139. Car has about 22k on it. Has a very slight rough idle, but it is very, very slight. Question--Can I buy a spray can or two of carb/injection cleaner and spray into the throttle plate area to clean it? Or do I truly need the $140 fix? Thanks.