06 lsj cobalt ss issue. Please help!
 

I recently changed my spark plugs, and now one of my cylinders appear to be misfiring. I replaced the ignition coil boot, replaced spark plugs, no difference. The only code I have is p1133 which is for an o2 sensor. My car will idle fine, but once i give it gas it has a flutter that sounds similar to a boxer engine. Any help would be greatly appreciated.

If it is misfiring like you say it should easily be enough to set a misfire code along with flashing check engine light. Is there a chance you somehow altered the connection of the wires going to your ignition coil or damaged the coil itself?

did you check the gaps of the plugs before you put them in?

and was the code there before you swapped plugs?

Code popped up when I drove it back from the dealer who I got the car back off of...changed the. Coils and plugs once ran like a dream for like a day then it started back up again.