Im just putting in my two cents here..........last summer I had the same type of problem you are talking about for about two months, got so bad the car would die when coasting in traffic. I replaced everything I could think of, never getting any codes from the dealer, and finally took the throttle body assembly off, and cleaned it and the maf sensor. Everything was filthy, be careful not to get any cleaner directly on the maf sensor. Anyhow, has run fine ever since. Might help, good luck.................

I just got it back from the dealer and they said a bad ground connection from the batt. to the computer caused the problem. Its been running good so far... wish me luck!

Problem solved!!! As its turns out it was a bad computer!

One thing you guys haven't mentioned is the EGR Valve. Sometimes the valve gets crap in between the valve and the seat which causes a vacuum leak. Check it out.... maybe worth a try. I had this problem on my gran prix.

Steve