check your mass airflow sensor, and basically anything that has to do with your air-fuel ratio, but the MAF is a big one. it might fix itself after 20 seconds because the engine gets warmer and when it gets warmer there is a different fuel ratio involved
also, did you get your car washed recently? or was your car exposed to water at all, make sure your DME/ECU(the computer) didnt get wet, and if it didnt, maybe your spark plugs got wet..
hope that was of help
PS: to bypass your mass airflow sensor, i dont know which to pins exactly, i did it before, but disconnect it, and take the connector and put a paperclip that connects 2 pins.. but just to test if it is the problem, unplug it completely and see if it helps(unplug it, dont remove it)