my car sputters on cold starts every once in a while, dunno why though.
maybe you have an ignition coil going intermittently. A while back i used to get random misfires sometimes as well as an occasional cel that read misfire when i got it scanned at autozone. Since then I've gotten all four ignition coils replaced and have never experienced that again.
edit : i see that you said you replaced the coolant temp sensor, I noticed my car sputtering after i replaced mine with the green one. again i dont know why..