One problem related to check engine light on has been reported for the 1999 Audi A4. The most recently reported issues are listed below.
Was driving approximately 30mph when the vehicle stalled out. Engine check light had came on & then off before stalling. Towed to dealer. Mechanic informed owner the air intake hose was detached & proceeded to reattach the hose. The stalling happened before on 12 Sep 1999.