Idle Control Valve

Hi,Could somebody please tell me, is the Idle Control Valve from an 1992 E34 M50 supposed to buzz when the engine is running or only when the ignition is turned on before the engine starts.
Thanks Ian

pretty sure its all the time, but you usually wont be able to hear it when the engine is on obviously. sorry i dont have an M50 in the shop to check at the moment

Thanks for the reply, I started the car the other day with the air filter box out and touched the idle control valve, couldn't feel it vibrating, it buzzes with ignition on, cleaned it and checked the resistance, all within spec, car is stalling as you stop when it has been parked for more than ten minutes after being at operating temperature, checked the sensors all in spec except for coolant temp. sender so replaced it, 02 sensor replaced recently, stomp test does not work on my car for some reason. Bentley manual says ICV should buzz while engine running
Thanks Ian