Need help...engine dies while coming to a stop

I have a 1997 A4 1.8T FWD. The idle on it oscillates up and down when I take it out of gear while coming to a stop. Sometimes it will die and others the idle goes down to the point where the lights go dim and the engine shakes. When I come to a complete stop and let it idle, it is fine. The other day the speedometer stop working and light magic the idle was fixed. Now the speedometer works again and the idle problem is back. Any ideas?

My friend says this :
I had exactly the same problem recently on my car as well - It happened shortly after i'd beed through a car wash - it turned out to be the idel control sensor - it had got damp and basically everytime i lifted of the accelorator the engine dropped to zero revs and died - i had to left foot brake and keep my right on the accelorator to keep the engine alive - a right pain in the backside - i had it cleaned and it has never been a problem since, and the engine idles perfectly now at 975rpm. I thought it was going to be a big problem as everybody was suggesting my throttle body may need cleaning or to be replaced but as it turned out it was a very minor problem and easy to sort - hope this helps