On the 98/99 turbo models I would first check for air in the fuel lines. The surging/bucking is a symptom of deteriorating o-rings allowing air to be drawn in. This is a very common, almost universal, problem on the turbo cars. I've not heard of this problem on the non-turbo, but it's very easy to check. Start the engine, open the hood, and look at the clear fuel lines. Lack of bubbles running through the lines would be a good thing...

- JimY