I have the same problem as the car gets older. It was very severe this past winter, given the cold, dense air. I think it was like adding an intercooler, cause I had some serious power, along with some serious bucking at 60-80km regardless of rpm. I changed the distributor caps and it helped a little, but what made the biggest difference was a fuel injector cleaner. Try a bottle of this product:
http://www.lucasoil.com/products/display_p...atid=2&loc=show
It's supposed to be a fuel injector cleaner/upper engine lubracant. The smallest bottle cost me ($6 Canadian) and its almost completely stopped bucking since then. It might be as simple as that... Let me know if you get the same results, cause it just warmed up here and I believe that has something to do with it as well. I use 89 octane BTW.
The first time it started bucking I replaced the oxygen sensors and that helped a great deal as well. (220,000 kilometers on car). The ride is much smoother since then and the low rpm chocking has gone away (2-3 years now). It's a bit-ch to change them yourself, unless you've got an entire day and the proper equipment. If so check out the following site. (I mention oxygen sensors cause I now get about $5 more milage out of every tank since then and a far smoother ride, so well worth the cost).
http://oxygensensors.com/
Let me know how you make out, especially with the fuel treatment cause I'm very curious. Good Luck!
Regards,
Cure