whenever i'm sitting at a light or at a stop in general with both the clutch and brake pedals engaged my engine rev hunts (idling up and down) as if theres a vacuum leak or something but when i let the brake out it stops. any ideas as To what it could be?

 

The ECU is programmed to cut the injector pulse above 1,200 rpm, this is because it know you are slowing down and to save gas it kills the fuel to the motor.

If your idle rpm is too high for any reason and your at a light with the brake on then when the idle climbs above 1,200 the fuel is cut. It then drops below 1,200 and the fuel come back until it raises above 1,200 again and it is cut again. Rinse and repeat!

It could be as simple as a simple idle rpm screw adjustment or as serious as a vacuum leak almost anywhere in the system.