Do you have a check eng. light on? If so there must be another code.
If not, check the hoses around the air intake/filter. Sometimes they get knocked off when checking the air filter. I have also see the filter box not installed correctly and pulling in unfiltered air and causing maf problems. I would pull the maf out and spray it off with some brake cleaner.
The knock sensor code will not cause ck eng light. Sensor is in valley under intake, but it will be ok. Resistance in a connector fools the pcm. On the pass side of the upper intake there are some connectors for the engine harness. There is only one white wire in these connectors. Cut the white wire on both sides of the connector and splice (solder and shrink tube!) the wires to bypass the connector, and it won't set that code anymore. No, this isn't hacking it up, there is a tsb on this procedure.