At cruise speed (between 3000 and 3500 RPM)the valves rattle,and they aint supposed to.A little more throttle or a little less makes them quiet.How do you stop this? I refuse to buy 89 or 93 octane gas!I have no service codes,no check engine light,and only 40K on this engine.My other 4Runner does this too,but my pickup never did.

 

How do you know it is the valves?

 

Pinging from low octane is caused by early detonation, has nothing to do with valves as far as I know. Sorry, not sure what your problem might be.

 

My truck used to do that too...it turned out to be a frayed timing belt, Might want to look into that, I thought it was too early for my timing belt but couldn't figure it out so I took it to a shop and thats what it ended up being...almost halfway torn through

 

Done any work on the top end of the engine lately? If so, I'll be you damaged one of the wires going to the knock sensor. I know that Toyotas are very sensitive to changes in the resistance of their wiring, and that their wires are prone to premature failures. Also, wire insulation sitting on top of the engine block is subjected to a lot of heat and often becomes brittle - if it cracks, many common chemicals (especially de-icers from streets) corrode copper easily.
Check the continuity and resistance of the wiring to the knock sensor, including the pigtail leading under the intake manifold if you can.
Good luck and let us know what you find.