Toyota Repair: 4-runner engine ping, denso spark plugs, coolant temp

Question
I have a 99 4-runner 3.4 V6 auto 155k miles. I have a ping(spark knock) under acceleration.  This only happens when it's warmed up.  I previously had a P0171 and O2 sensor circuit malfunction code(bank 2), I replaced MAF twice, rear O2 sensor, ran lots of carbon cleaner, did full tune-up, coolant temp sensor and it still pings.  The first replacement MAF cured the problem for about 800 miles then it slowly came back and is worse than ever.  Other than this the truck runs great, was getting 24 mpg now 21.  I suspect that it was running lean, but even though its not now it still pings.  Please help if you can, the local dealers won't even look at it because the check engine light won't come on. thanks

Answer
The check engine light won't come on for engine knock.

In this order I would:
Clean the idle valve, throttlebody, and EGR valve by hand. With a good cleaner/lubricator, and a wire brush that will let you in. The EGR valve being key. (The other 2 are just proper maintenance.)
De-carb the combustion chamber with a *real* cleaner. They are probably filled with carbon. Use something like Seafoam (follow the directions for it exactly, do it three different times using 1/3 of a can at a time.), or flat out water injection. Nothing will destroy carbon deposites, and raise the effective octane level higher, and quicker than flat water injection.

You need to intall the correct temperature NGK, or Denso spark plugs. Personally. I would install NGK part number 3967, or it's Denso equivilant. (Replace every 3-4 years).
Regardless of what plugs, or how new they are. I would still ditch them.