It may also be sucking in air.

If ur car has under body panels, remove them for a period of time. Little puddles on the ground could help point out any leaks. The panels do not let any oil or fuel drip on the ground.

Go around the fuel path and tighten all clamps on the fuel lines.

I would guess that, after the temp goes up, the system pruges the air in the fuel lines and the car smoothes out. Also, when the car heats up, the rubber seals better and prevents air from getting into the system.

U may want to consider replacing all rubber hoses in ur car's fuel path. If u do replace the rubber hoses, u may want to retighten the clamps again after a few days.