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 like magic the idle was fixed. Now the speedometer works again and the idle problem is back. Any ideas?

 

check for vacuum pipe leaks and clean the throttle body out