Hi
I purchased a 06 Impala LT back in October. Over the course of that time I have had to return it to the dealership going on 8 times, all for the same issue. What happens is I will be driving along and the cars check engine light will come on followed closely by the service traction control followed again by reduced engine power. At this point I have no throttle and sometimes the car will have this very very bad shimmy. Also at night before it happens and after all the lights are on the lights in an out of the car will dim, undim, dim, so on. When I let the car sit for a short time or overnight sometimes the lights will go away for a short time(long enough to get to work a couple miles away, or hurry home) To my knowledge they replaced the throttle sensor, the computer, and have entered new codes into it several times. Any advice or ideas would be more than welcome. I don't really know much about cars, but I saw these forums and figured it wouldn't hurt to seek advice.
Thanks, and sorry for the wall of words.

 

It sounds to me like you need either a reprogram or a replacement of the pcm. I don't know what computer they replaced, but the symptoms sound like that of a bad pcm or bcm