2007 cadillac cts sputtering at slower speeds as well as surging

Possible dirty throttle body/plate. Start at the parts store and get Throttle body cleaner. While you are there get some Mass Air Flow sensor cleaner (both very specific and should not be interchanged) and clean them both. Good idea to clean these from time to time. I do this as part of my fall routine...new air filter, oil change, wiper blades.

The flashing light means the problem is serious enough to cause damage to the catalytic converter. Have the computer scanned for trouble codes to proceed. And get the plugs replaced.

Sputtering. What do you mean by that? Lack of power, a specific noise your hearing?

Too many things it could be with a burn car. It is very hard to give a proper diagnostic evaluation without being able to put your hands on the vehicle. You probably still have some sensor or component issues. I recommend you download the FSM at http://foxed.ca/
That will give you the diagnostic procedure.

Here is what I would do I would get carb cleaner and clean the carberator really good and depending on what happend there I would get a set of hotter burning spark plugs after carb cleaned then I would see if it still makes sputter and then all I could think of from there would be taking the car in to see if there is new updates that can be downloaded on the computer of the vehicle I once had a problem like that and got computer updates and worked like a dream after words they can usually be downloaded at the dealer ship but they charge for the updates and you should ask if there is any first but in the end when I did that problems solved better gas milage and smoother running engine

Could be your cat is clogged up

First when was last tune up? that's a place to start. But for the sputter/miss sounds like a case of moisture/condensation in your fuel. Not necessarily bad gas but with big temp swings moisture and condensation build up. Try running a bottle of STP gas treatment through and see if that helps.

sounds like you will have to replace the ignition module which is where all the plug wires attatch to the coil packs.

to me it sounds like your just about to put water down your exhaust mate or your rings are binding up. I recon dump your oil and run diesel oil from now on and reset your timing belt before those new spark plugs end up in your lap.

My 2003 CTS would not start on the first, second or third try after filling the gas tank. Finally after several months of this occuring every two weeks a check engine light came on. It was the evac purge valve. Tom