Bob, that's not the exhaust solenoid. It's the one that controls the secondary air pump. If your exhausts are playing up it's at the back.
Probably
C
Brilliant, thanks. With my car, the valves often will not close for a few minutes after switching sport off (or the revs go below 3000), often needing the car to have stopped before they close. Both valves move well enough manually so I guess it is the solenoid (?). If so is it something I can change myself easily enough?