He used to drop into my chambers once in a while to smoke, and was first-rate company. When I gave a dinner there was generally a cover laid for him. I liked the man for his own sake, and even had he promised to turn out a celebrity it would have had no weight with me.
The owners manual on every vehicle should state how often the manufacturer recommends that you tune up cars, but as a general rule it is every two years or 30,000 miles, whichever comes first. Driving under extreme temperature and weather conditions will make parts wear out faster, however.
beyond the plugs, air filter, cap, rotor, wires and valve adjustment the tune up usually includes other services like brake inspection, transmission fluid change, oil and filter change. those are not responsible for the idle problem but should be done every 30,ooo miles.