...and how easily can it be replaced?
My car flashed a check engine light for a second or so, when I was at a light, idling. It went out as soon as the RPMs increased when I accelerated. I checked the code anyway and it pointed to the something-or-other (DISA) valve.
What the heck is it? What does it do?
FWIW, the car runs as strong as it ever did...no performance problems at all. Fuel mileage is still at 24 mpg city, so it hasn't affected consumption, either.