I don't know if anyone else has had this issue or would benefit from this experience, but here it goes anyway.
There is a stretch of road on my way to work about 1/2 a mile long. It's a gentle downhill. I can often take this stretch at 55 mph pulling 65-70 mpg (remember I said downhill). Every once in a while the car would feel like it was turning off. The mpg would peg at 99, and the car just seemed to die. If I gave it just a little bit of gas nothing would happen, but jut a little more it would cut back on and be about 60 mpg.
I spoke with the one ASE Certified Master Mechanic at our local dealership last week. He had no idea what it was, but was interested in finding out. I do not know who he talked to at GM about it, but he called me Friday and told me the answer.
Simply stated, I was getting too good mpg along that stretch. He said that the ultra high mpg was triggering the computer to do a fuel shut off. He said this is a rare issue, and only seems to happen in the 5 speed with the XFE "treatment". It's not a problem with the car, and is harmless.
His suggestion was that I pull it out of gear and roll, or just take the 60 mpg and be happy. A Cobalt is simply not ment to cruse at 65-70 mpg.
I just thought this was a little funny.