Knock Sensor would be easy to diagnose, the ECU will spit out a code. I've had one go out and this doesn't sound like one. Have you checked ECU for codes? Also start the car and disconnect each coil pack to see if the idle changes to see if one is broke (or possibly narrow down a bad injector) Also ohm check the injectors. If you need a coil pack I have several that I will give up for $20.