what is typically included in a tune up?

What is your question?

170000 miles- last tune up at 120,000, slower than usual and is running rough. dealership offered to just replace spark plugs for $500...but I am sure there is more that needs to be done- so am wondering what is typically done with a tune up? Thank you

How long has your 2008 Mercury Mariner had this problem?

a few weeks