The idler arm is one of the components of the steering linkages which is essential to the steering gear functioning properly. If the connecting ends of it are loose, then you'd have some free play in the steering and tracking of the car. It may have just enough wear in it to be noticeable on the rack, but not enough for you to notice any problem while driving the car. The best way to check out the extent of the problem is to take it to an alignment shop where they can check it out for you and advise what parts, if any, are needed at this time.
Because this is a safety item, you should have it checked out as soon as possible so that it can be replaced (if needed) or verified OK. Here is what I recommend you do. Go to the Car Talk mechanics file at http://cartalk.com/content/mechx/find.h
tml, enter your zip code and there you will see consumer recommendations for reputable shops in your area. Call the highest rated 2 or 3 of them and ask them a ballpark figure for the repair you need. look for shops in particular that specialize in steering and suspension problems.