Idle control valve buzzing noise usually down to it being ditrty and in need of a clean. Take it off and sray carb cleaner in it and give it a good shake to agitate the dirt thats built up in there, dry it out with some compressed air if you have a compressor or just let it drain before refitting it.
The EWS system is indeed the cars security module that controls the locking/unlocking and reads the transponder in your key when its put into the ignition. There are two distinct systems in a key, one is the lock unlock system that operates with the buttons on the key, this is contained inside the fob on a small printed circuit board on which is a rechargable button battery that powers that part of the key. The battery gets charged by the car when its active in the ignition and engine running. Bear in mind these batteries are getting ancient now and nothing lasts forever, it may have lost the ability to store a charge. Resting the key overnight or longer on a domestic toothbrush charger will surprisingly charge the battery. Give it a try and see if it comes to life. The key if charged may need resyncing to the car to get the lock/unlocking buttons to work correctly. Threads on here to show you how if you have a search.
The second system within the key fob is the transponder chip that contains the cars identity that will be read by the EWS module when the key is inserted in the ignition, it will look at the info on the chip to verify the key belongs to the car and a second code called a rolling code that the car gave to the key the last time it was used in the car. If these match it will release the starter motor and allow the car to start.
The transponder has no power supply in the fob, it works by BMW Black Magic and a small aerial that is contained in the plastic surround around the ignition key switch.
EWS module is located behind the outer footwell side panel on a right hand drive its on the right hand side, not sure if left hand drive cars will be the same, maybe look on the left if its not on the right. Module is a small white oblong box held in by one nut.
If you take it out it has one multi pin connector. Nothing to really see if you take it apart other than a printed circuit board, if you spot any blown componants on it or maybe water damage/corrossion then maybe look for a known good replacement. Replacements need coding to the car using software such as NCS Expert. When sourcing a replacement it must be the same part number as the one it is replacing.
www.bimmerforums.co.uk
