$700 craigslist steal 1984 318i rough idle issue

[Blackout]

Why EmTen EmTwenty?

[EmTwenty]

Whats up r3v! So yesterday I bought a 1984 318i off craigslist for $700 bucks. I bought it knowing it had a high idle and wants to die when you put it in drive. Otherwise once its past 3k rpm it runs good. After doing some troubleshooting all day we came to the conclusion its a vacuum leak. We sprayed starter fluid on any possible leak with no avail and cleaned the IAC. We noticed that when you pump the brakes multiple times the idle dips down and it wants to die. So we think it maybe has a brake booster vacuum leak, or the check valve has gone bad. Just seeing if anyone has any suggestions on what it might be. Your input is much appreciated!

$700 bucks at it's finest!