for some reason as my idle changes, or when I turn on the AC the brake pedal noticeably fluctuates up or down, even subtle rpm changes. I've never noticed this before. Also if I park on a hill and kill the engine, I almost don't have enough force to hold the car in place before pulling the e-brake. Any ideas on what to check, or is this normal?

 

Sounds like a bad vacuum check valve or a leaking booster. Do you hear a hissing noise when your foot is on the brake?