Brake Booster Issue

Hello all , I just picked up a second addition to our home a very nice 71 240z from one of our members , the prob is the brake pedal is very hard when pressure is applied just like when the brake booster has gone bad but it doesn't raise the idle like one of my past z 's did when the booster went bad. Could it still be the booster or maybe the checkvalve? Any suggestions would be great , thank you