As ImperialCrown stated we need to know specific make, model, year and engine configuarion, 4 cylinger, V6, V8, and some images of the vacuum lines in question to make a reasonable, accurate diagnosis.. . . Does anyone know why when I connect the 2 vacuum lines 1 from plenum the other on to of throttle body the engine cuts off on idle. Do these lines go to a vacuum pump Defective? . . . .
Now if you wanted a "wild guess" I would say one of the suspect vacuum lines might be connected to the EGR valve. Fully activated EGR (exhaust gas recirculation) will stall an engine and stop it from idling. But again just a guess. Give more detailed information as requested.