When my car is in idle at a traffic light/stop sign, it will stall out and cut off, why is this?

Does your check engine light come on? If it restarts right away, then runs normally otherwise, you may have a defective idle control valve.

The butterfly shaft bushings in the runner control system can leak unmetered air and cause the engine to stall. You have to replace the lower intake manifold if this is the problem. The first thing I would try is a smoke test. You could diagnose this by injecting propane around the shaft bushings.