new master cylinder now super high idle?? WTFF

[schmall's supe]

so i just picked up an 89 and it idled fine put new brake master cylinder in and the idle is now at like 4000 what the hell. When i turn the car on and off, letting it run for just a second, i hear hissing like air escaping from the large black thing the master cylinder sits in if i remove that vaccum hose from the intake manifold and put my thumb over it, it still races up to 4000 when started but when turned off it doesn't hiss at all. now with my thumb not on the the hole it races even higher. whats going on? another leak or what??

 

[DaddyBuiltRacing]

You have a vaccum leak. Is the hose coming from the intake manifold to the brake booster (black thing the mc sits on) connected tightly?

 

[schmall's supe]

yes the hose is tight, im afraid the brake booster is leaking or malfunctioning some how, are they difficult to replace or is there some quick fix to this?

 

[DaddyBuiltRacing]

Your booster could be going bad. Spray some carb cleaner around your hoses to try finding the leak.