To conclude this thread, in case this helps someone else some day:

On a shelf in my shop, along with many other tools, there is a compression gauge. Why I didn't start with that is beyond me. This is just a reminder to anyone else thinking of ignoring the K-I-S-S principle (keep it simple stupid.)

Cylinder #3 is dead. Not sure exactly what but it doesn't matter. 4Runner parked until I have time to rebuild the motor or have a better idea. Ugh!


My mechanic told me that another sign I missed was the way the starter is not consistent in the way it turns. Fast, then slow, fast, then slow...

So, thanks again!

 

Just putting it out there, but it's probably your valves. Toyota recommends adjusting them every 90k miles, but most people don't bother because of the work involved (22RE can be adjusted in 30 min, 3VZE in... about 2-3 days if you could shim delivery times). A leak down test could confirm this.

I had #3 go bad as well, ran great after valve adjustment. However, if this issue just came out of the blue, it's probably not just an adjustment, but a valve job needed. Not quite a full rebuild but close.

 

Yeah. Out of the blue and sudden. Half an hour of highway driving after adding Rislone to the oil. I believe it is probably valves, like you said and my mechanic mentioned as the possible culprit, and too much to take on at the moment with the list of other projects having higher priority. With almost 300k miles, I may just hold off a bit and rebuild.

So, although I can't assume that the Rislone caused the problem, it is odd that it happened so close to adding it. I can't remember the exact mileage, but I had the head replaced within the last 60k miles or so after it cracked on a particularly cold Wyoming morning.

This is gonna bug me now and, if I can break away from other projects, I may do a leak down test before a full dive into rebuild- another thing I've never tried.

Thanks for your help!

 

thanks for the updates....pretty rare to actually read what the solution turned out to be.

 

Maybe it'll help someone else diagnose.