What is the idling jitter of Ford Mercury commercial vehicle engine?

When idling, ECU should adjust the ignition angle, which will cause engine jitter.

For example, the ignition angles -3, -2,-1, 1, 2,3 gradually increase in numerical order. When knocking is found, ECU will immediately adjust the ignition angle again, and then adjust it from 3 o'clock to -3 o'clock. Such a wide range of adjustment will make the engine slightly shake.