Balking at Highway speeds

I am having an issue with my 04 Grand AM v6. When driving at highway speeds (65-70mph) the car will sometimes 'balk'. Don't really know how to describe it. It is almost like the A/C kicking in on a smaller 4 cylinder engine if you know the behavior. It is freqent enough to be annoying and the dealer techs say they can't find anything (although I doubt they really tried hard to find it). The engine accelerates fine and all, this appears so far to only be at the above speeds, although to be fair I only drive it 24 miles (one way) to work and of that over 20 is controlled access highway.

What could be causing this behavior? As I have said it feels like my old corolla A/C kicking on but it can be worse every once in a while and sometimes it might do it 2-3 times in quick succession although when that happens it is not as bad as when it only does it once. It happens with A/C on and off.

Any opinions or further questions for clarification?

Thanks,

Mike

does the engine pull or rev when this happens? does this car have ram air? is there any plastic air dams in the front, under the bumper, broke or flapin around? my 99 had a strange noise in front and it turned out the plastic air dam, under the bumper, was broke in the center and the noise was droveing me krazy so i tore it off, kept the side air dams that curve to keep snow away from tires and wind i guess. Maybe these will lead you to the culpritt. Good Luck and Welcome to Automotive Forums.

Thanks for the welcome.

The engine does nothing else as far as pulling or revving. When I took it in, I had to tell 2 people three times that it was NOT surging, quite the opposite. The front body moldings and underside air dams are all good. At first I was wondering if it could be something like that, but I find nothing loose or missing. Like I said, it is like a small engine having the A/C kick on. You kinda feel the car pull back (or at least at highway speeds, kinda feel a 'bump'). Not horribly, but it is noticable.

Just trying to find a place to start when I take it back again. Engine, Transmission, ....???

Thanks,

Mike

i guess i have heard people talking about the AC causing problems at highway speeds. But you said it happened w/out the AC.... Could be the Overdrive kicking in and out, but on such a newer ride I would doubt it was the transmission.

I had a bad wiring harness(93 GA) to the the trany once and it took 10 trips to the dealer before the found and fixed it, with black tape... the 11th time they replaced the harness(i hate warrenty work) but by then the transmission was about dead from the constant shifting up and down in OD.

It could just be one of those bugie things that no one else has noticed yet or an anomilly that will never be found until something breaks.

It could also be a bad coil pack. I had an intermittent buck when putting a heavy load on the car, usually uphill, first thought was a bad injector but later investigation into the problem turned out to be a bad coil. Just another thing to check...