My Car is Shuttering?

you already figured out the problem, but not why, pull the plugs intil you find the one that is the problem, if its hard to tell, then pull and replace all of them with new ones, and take the old ones to a mechanic for ysis. I believe you have a plug, it is oil fouled (likely) or gas fouled (less likely) but if the vehicle is not driven on the highway much, or you use cheap crappy fuel and do not change the oil much this may be part of the problem (Im only guessing at this point, on why a plug would foul out so quick)