How many miles do you have on your car? If you're approaching 80,000 or more it's always a good idea to replace the valve springs if they're still stock. They're cheap and pretty easy to do if you have the right tools. The only way to REALLY tell if you have bad valve springs is to take them off, take them to a shop, and have them measure seat pressure. But it's not worth your time and effort. Just take them off, go get a good set of Comp Cams springs, take them to a local shop and have them all matched up (you may need some shaved or shimmed). Put them on and you'll save your valvetrain 10's of thousands of miles, and a lot of headache in the future.