This happened to me ages ago with my GC8 and it happaned to be my spark plug at the time
tho the spluttering only lasted few mins and when away, we park the car aside for few hours and came back it was all fine :S
I changed my plugs the next day and there was sign of water on and around it...
My ilde also hunt a bit when its warm tho that may have been the shitty
MAF