I've found it prudent to swap out plugs every 30K on the 'Tour. OK, it's a little aggressive, but I've learned to be that way with my cars an it hasn't failed me yet.
Basic maintenance can do wonders to a car that's not performing up to par.
JaTo
e-Tough Guy
Missouri City, TX
99 Contour SVT
#143/2760
00 Corvette Coupe