Might be an adjustment to the fuel distributor, maybe CO.
Might be set very rich and then when the loop closes the 02 sensor compensates
some for the overly rich condition.
I don't see it sputtering though. (scratching head)
Check the CO or FPR current when the engine is cold
Are you using platinum spark plugs in it? Try some Bosch tri-electrodes
(W7DTCs) and see what that does for it.
Could also be a weak coil.
All new ignition pieces?
New Spark Plug Wires? Might be defective but working better when they warm up.
just some thoughts!
Before you criticize someone, you should walk a mile in their shoes. That way,
when you criticize them, you are a mile away from them, and you have their
shoes. Frieda Norris