More than likely you have an injector stuck open.
There is probably one that leaks a little after the engine is shut off and all the fuel pressure leaks down that one cylinder.
Sometimes you might notice a slight misfire at startup. It it doesn't misfire long enough for the misfire monitor to pick it up.
What I've done in the past to find those is remove the injectors from the intake leaving them in the fuel rail. Cycle the key on and off and back on a few times. That will pressurize the fuel system.
Then look at the tips on the injectors. If any are wet those are the ones leaking.