There is a test for the recoil spring... With the chamber empty, pull the trigger and hold it. Raise the muzzle to vertical and pull the slide back then let go. The slide will want to move forward, but will be unable. Slowly lower the muzzle toward horizontal, the slide should return to battery by the time you get to 45* elevation. If you have to go nearly horizontal, the spring is too weak.
You might also check for crud under the extractor, or gummed up extractor.