Okay, if the parts were replaced for age and not failure but it was running good then they may not have touched the plugs to prevent issues. The owners manual info on that vehicle shows the plugs are a 60,000 service item. So at 112,000 if they were not changed they could easily be the issue. However they are known for the wires and coils as well.
To change them requires that the intake plenum be removed to gain access to the plugs, like many newer cars. The book shows about 2.5 hours of labor for the job. It's hard to say if they are worn out or if something else happened, What you might want to do is take it to a different shop for a second opinion. They should be able to tell if the parts were replaced or not. Might even ask a couple other places for prices on the same work. As I don't know the thoughts of the other shop I don't know what they did, however if they charged to for the tune up parts and now they think those are the problem now, it would depend on what they warranty and what they showed on the bill.
If you want to see what it takes here is a video on it. Shortened a bit in editing so you don't see the entire process.
Thursday, November 21st, 2019 AT 6:25 PM