So, June of 2012 I was driving during the summer on with my AC blowing and my car started to make a stuttering sound at idle and dropped down to around 600 RPMs. I took it to the shop and all they did was replace my timing belt and the engine temp sensor. I got it back and it did the same thing for many months while it was still hot outside. Once winter hit, it stopped stuttering but I was experiencing turbo lag. In December while I was driving home on a 20F night my CEL came back on and the code told me it was my CTS. I replaced that, reset the code and my turbo lag was gone. About 50 miles later the CEL came back on and the turbo lag came back as well as my front radiator fan runs all the time very loudly. My car runs fine, the turbo just doesn't boost as high as it should and it idles around 1200 when I first start it after it has been sitting. My CEL is still on, and it's the same code (I can't remember which). Any thoughts at all? Thank you for reading.