Four high probability causes, in roughly descending order of probability:

1. Sticking air flow meter/fuel control plunger.

2. Sticking system pressure regulator, causing fuel pressure spikes.

3. Momentary loss of electric heating power to the control pressure regulator, aka warm up regulator (WUR), allowing plunger movement in the rich direction.

4. Deterioration of a flexible hose in the fuel return line, that intermittently blocks return flow, causing a pressure spike