One problem related to steering idler arm has been reported for the 1999 Ford Expedition. The most recently reported issues are listed below.
My husband and I were driving our 1999 Expedition at 40mph near my home (ramona, CA),left front idler arm snapped causing violent front end shaking, vehicle was out of control. If I had been driving on a freeway or any higher rate of speed my husband and I would have been killed. We are very fortunate to be alive. We were able to stop the vehicle and the road we were traveling had no traffic at the time. The road was a rural back country road (vista ramona, near hwy. 67. ) ramona, CA.