The idler arm and control arm are two different components. If it is indeed play in the idler arm that is contributing to your problem I have listed links to the parts. The first link is a kit that you can purchase and the second link shows a diagram of your front suspension showing all of the components.

http://www.performanceproducts4benz.com/product.asp?pf%5Fid=P46%2D012&dept%5Fid=6390

http://www.performanceproducts4benz.com/diagram.asp?diagram%5Fid=22

If you decide to purchase anything from the above diagram I would check with Phil at Fastlane first. He'll be able to get them to you much quicker than the company in the links. I just thought a diagram of your suspension might make diagnosing your problem a little easier.