If it was pinging with any predictability it would be a lot easier to diagnose. I've been searching around and other suggestions I saw where to replace the fuel filter and clean the MAF. Both are easy enough to try.
I have to do some research on the knock sensor but it's possible the ECU could detect knock and retard the timing but not cure the problem so the knock sensor isn't necessarily the culprit.
One thing I forgot to mention. In doing general maintenance I noticed oil residue inside the intake tract just ahead of the throttle body. It's coming from the fresh air side of the PCV system. Since air is supposed to flow into the cam covers via this hose, nothing should be coming back out so something is amiss. It's not a lot of oil, but it shouldn't be there at all. I checked the other PCV hoses and they all look good. There is no oil residue on the vacuum side of the PCV system either. Not sure if this could be related to the pinging but...
