I don't think it's sensor, although they commonly go bad.
Have you POSITIVELY checked or changed the PCV hose where it attaches at the BACK BOTTOM of the intake?? Don't say you've 'checked it' if you haven't crawled under the car, just screwing yourself. Look at the last 3-4 inches before the hose goes into the intake and FEEL it, if like bubblegum you need new hose. The most common vacuum leak on these cars.
To check the brake booster check valve. Start motor up, let it warm at idle. Shut motor off and then within 5 seconds step on brake pedal ONE TIME, see if you have soft pedal then. Bend close and listen for a short soft hissing sound too. If check valve is working, you will get soft pedal up to 2 or 3 pushes and the hiss those 2-3 times, then it will get hard and the hiss stops. If hard the very first time you push it and no hiss then check valve or booster or hose is bad.