error code p0325

[fridge67]

hi i have a 2011 mk3 foucus 1.6 ti-vct thats been playing up. used forsan and it gave me the error code p0325 which relates to the knock sensor. having a quick look i can see i have two fitted to the block behind the inlet manifold. i couldnt see any obvious damage to wiring etc. how do i tell  which one of the two it is  or is it not the knock sensor itself but somthing else making the engine knock and the sensor just picking up this. The engine managment light is not on. sometimes the car seems to lack a little power when pulling away and sometimes will stallout. the plugs leads and coil pack are relatively new. any thoughts would be appreciated