Engine knock sensor code

Well Auto Zone said my service engine light was due to the engine knock code!!!!
I have been running 87 octane in it, and manual says we can run 87 and might be some noticable lack of performance.
I get NO pinging and car runs great!!
Going to have a mechanic (private) shop run a check.

How about ?
EGR valve
Oxegen sensor

Input greatly appreciated.

My 98 is throwing out a spark knock code and the dealer said their computer shows no spark knock. Go figure. I'm trying to find the time to leave it at the shop right now.:cry:

An easy test is to put a tank of good premium in it (like it's supposed to have) and see if the problem goes away.