I have a 2007 CTS. I switched to premium fuel then back to regular. Almost immediately, it started misfiring. The check engine would periodically flash for a few seconds then go off. I went back to premium again and the problem stopped. I was running premium for six months and never saw the CEL again. Due to the gas situation in Texas, we had no premium and I had to fill up with regular and once again I felt it misfire almost immediately. The CEL is now solid. I am going back to premium but I am concerned that the engine may be damaged. I only feel the misfire when I accelerate to around 60 and its very brief. It has never stalled. I dont see any smoke or anything. I just find this odd that a car would react like this simply because I used a different fuel grade. is this normal for Cadillac? Should I just let the gas cycle through or does it require attention from a mechanic?