Mitsubishi Galant Intake Manifold Replace/Remove

So My Car For Awhile Has Had A Broken Intake Manifold Bolt On The Top Two Main Bolts. And Also It Has The Intake Manifold From The Diamante...

What Would/could Cause The Intake Manifold To Snap Where It Connects To The Carburetor?timing Belt?motor Mount? Have Replaced It Once...

I Just Replaced My Intake Manifold With A Stock Intake, The Car Will Only Start If You Hold Your Hand Over The Throttle Body, The Car Quits...