Slight rough idle. RPMs fluctuate 150± sometimes. Surges at highway speeds.

Thanks for the quick response. As soon as I get more data, I'll post it. Without a definite code, the Service tech can't seem to give me a definite answer. All of the sensors, coils, etc. are original and have never been replaced. Updated 3-1-2012: Let Buick dealer keep vehicle for 3 days. They tried everything they could think of. They swapped out catalytic converter, MAP sensor, MAF sensor. Checked fuel trim and fuel pressure. No vacuum leaks found. The dealer called GM and they said sounds like a problem with the torque converter. I don't see how the torque converter could cause the rough idle. Maybe the rough idle is causing something with the torque converter but I don't think so. Drove the vehicle home. Now will have to see if Buick will give me some kind of direction. If not, I'll trade it in and get what I can for it. Updated 6-21-2012: Terraza finally set a code a couple of weeks ago. I checked it with my code reader and it was P0011. This indicates a problem with over advanced timing. I took it to my Buick dealer and they repaired it based on the procedures for this code. I got the vehicle back and have been driving it for over a week now and the problems are gone. No more surging or rough idle. Not sure why it took three months for the vehicle to finally set a code but it does seem to have been my problem.