After getting the 304 ECU code for a month (no CEL), I decided to replace the knock sensor. The part cost $130 from my local dealer (20% off list) and I had to purchase a 12mm flex socket from Sears to fit into the narrow space.

Well, using the Skippynet instructions, I managed to replace the sensor, although I needed the use of a young lady's hand to put the sensor back in. Any guy with average size hands, I cannot imagine how you can reach down there to replace the knock sensor. I have large hands, and it would have been impossible.

Oh, for people wondering how the knock sensor attaches to harness, there is a paperclip looking retainer holding the tabs in. Remove the thin metal band to replace the knock sensor. Kind of confusing reading it, but you'll understand what I mean when you see it in person.

As for performance, I do not notice a difference yet, but it was raining very hard tonight so I could not push the car.

Coincidentally, as I was driving home from the Sears (with my flex socket), my CEL went on. Pulled a code 903, EVAP canister. I remember driving through a very deep puddle (probably 4" deep). I've reset the ECU and the light still comes back on.
Is is possible the evap canister got wet and threw the error code? If so, will the evap canister dry itself out and the code disappear?