[rlith]

Since you only changed the rotor, I would change the cap as well.. Change the spark cables and spark plugs as well. Just because you saw it spark doesn't mean it's good. Get the vehicle scanned, that is your best bet. Drop some oil from the pan (lets say a pint) and see if there is any water in it. Also pull your plugs and crank the motor a couple of times to make sure that no water is in the chambers.

Start with those things and we can go from there on narrowing down the issues.