knock sensor?

what are the other possibilities? where are the sensors located?
as far as i know the car is all stock. but i got it used
any help is greatly appreciated.
Haven't replaced the ks myself but doesn't look too bad.. removing the intake isn't hard either.
By the way when you change your spark plugs i found it frees up another few inches by removing the coil packs to give you room to reach down in there.


