Sounds like your idle speed is set too low. It's also possible you have a bad fuel pump, clogged fuel filter, or clogged air filter. The fuel and air filter are both relatively easy to replace. The air filter should be changed every year. Your fuel filter should be changed every 2 years /20000 miles. This could also contribute to lose of power going up hills. You could also try running the car with a full tank of premium gas and a fuel injection cleaner. See if that helps.

If you have the equipment, you should have the compression checked if your problem doesn't get fixed by replacing the filters and setting the idle speed. If your compression is off, you could have a blown head gasket; but I think that is the worse case scenerio.

If you've never replaced your timing belt, have that checked as well. If your ignition timing is off, you'll definately have a rough idle; then your car would eventually stall.

If you don't feel comfortable checking and/or replacing any of the items I mentioned, have a qualified mechanic check it out for you.
Good luck!