Vacuum leak makes it run better?
 

I have a 91 corvette with the L-98 tpi engine. I recently changed my power brake booster because my pedal turned rock hard. When I was finished replacing it I started the car and it stalled almost instantly. I took the vacuum line off the booster and it runs just like normal. I plugged the line as the dealer suggested to test it out and it stalls instantly. Im told this is completely backwards than it should be. Any ideas on what to do or check next? Any help would be appreciated.

Will it run with the vacuum line either connected to the booster or plugged if you hold partial throttle? If so, I'd suspect the IAC isn't opening.

it will run if I connect it to the booster as long as I keep it at half throttle or so. The weird thing is that it ran fine before I started this project I just didnt have power brakes.

The IAC is essentially a vacuum leak itself. I'm guessing what happened is that the IAC had closed completely attempting to compensate for the booster leak and is now stuck shut, as 94z07fx3 suggests.

But the part that I don't understand is that it ran perfect before I pulled the vacuum booster, but as soon as it was all together it would not run. Which confused me and made me think I either messed something up or did something wrong. But I didn't change or take anything off other than that one vacuum line. Maybe just a fluke that it happened at the same time?

How long was the booster leaking? Your IMPRESSION is that it happened when you replaced the booster, in reality the IAC may have been stuck for some time, the car stayed running because of the additional air provided by the vacuum leak. That air flow is now closed off, if the IAC is stuck in the closed position you need to apply throttle to keep it running.

well my power brakes went out on tuesday after work. I drove it home which would have been about 20 mins. Then I replaced it the next day.

This might sound dumb... but if IAC is stuck open I could pull it out and try the tap method? Granted that I dont hammer it too hard to harm it?

Not really, the IAC works on a motor solenoid. You have to spin the armature of the motor to get the plunger to go in. Try this, pull it out (IAC) and start the car. Hold your thumb over the hole and watch the plunger. Experiment by letting more or less air into the engine. Does the IAC move? If no, it's bad.