My car has always run rich. It always stumbled getting into boost, so today I did a boost leak check. Low and behold, My Tb is leaking at the shaft seals and base idle screw big time. Would this cause my car to run rich and stumble?

Normally I dont drive the car hard, But today I beat on it a bit with a buddy behind me and the car was shooting out black smoke under boost and my friend said the exhaust smelled like gas. I smelled it too. My back bumper is covered in soot also.

My car is a 97 GST thats stock and has no mods. Any help will be appreciated.

Cheers

Yes boost leaks will make it rich.
http://www.vfaq.com has the fix in the intake section: Throttle body shaft seal replacement / BISS screw (you probably need a new o-ring)