It your under the 8/80, then they shouldn't be charging you a thing for warranty work. I would take it in, have the testing done, and see what they say. Or you could take it to an independent shop first, have them do it (some will test it for free, others will charge you 75-80 bucks), take the car to the dealer where they will still have to do the diagnostics to determine exactly what the problem is.
So, in short, just take it to the Ford Stealer and see what happens.
