Wierd stuff started happening with my SC when driving back to MI from KY. The best way I can describe it is that it was surging while driving at a constant speed, kind of like run,die,run,dierun,die........ in about 1/2 second intervals, if that makes any sense. It would get worse if i accelerated but seemed to get better if I decelerated. I was able to decelerate and then slowly feather in the throtle a few times and then it would go back to normal for a hundred miles or so, then happen again. The first time it happened I thought I was losing my trans from the violent on/off cycling. But when I pulled over it was still surging while idling in park. A couple of times while this was happening, but not always,I lost the tach, then when the engine went back to normal the tach came back.
I replaced the DIS, but no improvement.
The check engine light never came on.
Has anyone ever had this happen?