Sounds like what typically happens when the valve stem seals are worn out. On the OVP problem, it also starts hard, but the idle speed will be incorrect also, and most times you also have the ABS light on (dash light).
I'd inspect the spark plugs for signs of deposits being caused by worn or hardened valve stem seals. How many miles on it?
If you replace the spark plugs and then it starts OK for a week or so, then starts doing it again, probably the valve stem seals. Although I have had a few cars that acted this way and it ended up having resistor spark plugs in it, replacing them with the proper spark plug fixed it. You don't have any of these fancy spark plugs in it do you? Need to run the recommended non-resistor plugs, preferably Bosch Super. Or for that matter, it may be just worn out spark plugs.