Hello and Thank you for choosing Just Answer.
The newer Expeditions, Navigators and F150 vehicles are known for the wrnech light to come on in the dash. What I have found with most all of them is a faulty Electronic Throttle Body or ETB. The internal electronics go bad and it will cause all kinds of driving and accelerating concerns. I beleive this is what your dealer is reffering to and I would agree with them. Hope this helps.