I have an 02 grand prix gt I bought a few months ago. Recently on start up the car will shutter pretty violently and the CEL will flash but after about 15 seconds it goes away and the car runs fine. Afterwards there are no codes, I did have an O2 sensor code but now its gone. I have not had a chance to check the basics (plugs, wires, etc) but just curious to see if anyone else has had similar issues or any clues as to what it might be. Thanks.