The idler arm is a component of the steering system in rear-wheel drive vehicles with a steering gear box. The tie rods and drag link attach to the idler arm and rotate on its pivot axis. Typically on the right side of the vehicle in left-hand drive versions, the idler arm maintains the steering gear opposite the Pittman arm. By working in concert, these two components allow the steering gear to manipulate the steering on both sides of the vehicle equally. Rack and pinion steering systems do not use an idler arm.
As the idler arm breaks down, the tires may begin to show uneven wear or the vehicle may begin to wander in the lane. The easiest way to diagnose a steering gear related problem is to take the vehicle to a reliable alignment shop where a mechanic can diagnose the entire steering system and recommend any needed service issues. It is always a good idea to have a second mechanic perform a diagnostic service and compare the two findings.
Most idler arm preventative maintenance can be performed at the oil change interval. A simple greasing of the idler arm and related steering components are all that is recommended to keep this part of the vehicle in top operating condition. Most oil change facilities will perform this service at no extra charge, but this should be requested at every oil change to be certain it is being completed. This is also easily handled by the do-it-yourself mechanic with a grease gun in the driveway.
It is also a good practice to clean around the idler arm mounting bolts on the frame of the vehicle. Often, small cracks will begin to radiate out away from the bolts. In this instance, the arm should be removed and the frame repaired by a competent frame and body shop. Typically a few minutes with a welder will cure the problem, but some repairs require a steel plate be welded into position to back-up and reinforce the frame.
While online auctions have become the fastest and often the easiest place to find used auto parts, it is not wise to obtain critical parts such as steering parts from this type of parts supplier. The arc of motion is very precise in this case and the variance of even the smallest amount could throw the steering system out of order and cause the vehicle to handle strangely. Always purchase steering components from a reputable parts supplier and make sure that the part is made specifically for the correct make, model and year of the vehicle on which it will be installed.