I have a2006 Cobalt LS with the 2.2 in it. Recently it started to vibrate when idling and it would idol really high when first starting so I changed the spark plugs. When I changed the spark plugs there was some white residue on the plugs which someone told me was from moisture getting to my plugs ( not sure about that). After changing the spark plugs the vibration has gotten worse than before and ontop of that the car is puttering really hard from the exhaust when idling. Any ideals on what this is or what it can be it would be appreciated.