After driving about 250 miles today on the freeway, I was stopped in traffic on the freeway and my car just died. I tried to start it and the first time I tried it it was cranking but did not start. Then the second time trying it started. After I got it started again it was idling about the same as before, maybe slightly rough. But when the rpms are above 1k, the tachometer bounces. It would usually stay within about 300 rpms of where it should be, but the only time it was steady was at idle. Acceleration does not seem to have changed much. Side-note, yesterday we changed all of the plugs with new stock ones, which did make it run better. Anyone have any ideas? Maybe cam shaft or crank sensor? Also, there are no codes, and the service engine light does come on when starting, but it doesn't stay on.