I just fixed the same problem on my car, the wires in the harness were rubbing against the intake manifold. Look where the harness snakes around the manifold, you might have to dissect it, separate the wires, and reinsulate the whole thing.

Alex300DT- you deserve your moniker! Today the car was really acting up and so that gave me a chance to try your advice and it seems to have worked!!! I have simply pushed the harness up and away from the body of the IP so it was truly suspended in the air between the intake manifold and the IP and the surging went away. Had to go to work so did not have a chance to mess with it as much as I would have liked but things are looking up! Something in the harness must not be OK so I will have to take a closer look. Thanks again - what a great forum!