I just checked the distributor and the mount/adjusting bolt was loose.
Now I have reservation and think this problem is timing or in the ignition system. I tried varying the distributor within the adjustment range, but not positive results. Then I began to wonder about the plug wires and realized I don't know the firing order of this 4Y engine. Toyota 4 cylinders have had of 1342 or older Corona's were 1243.
I checked for the firing order on the engine but didn't see it on the manifold.

Since the distributor mount bolt was loose, I suspect the whole unit might have been removed and re-installed. Hmmm, could be of a tooth when re-installed. Another possibility.

Without a manual, I'm going to have to play around with this one.

Steve