99 a4 misfire

[steve5413]

Hi, I have a 99 a4 2.8 quattro. At a constant 30/40mph it either misfires or stutters. A friend plugged his machine into it and it came up with a fault relay 9. His machine was unable to elaborate on what relay 9 is? Can anyone advise me if we are on the right lines? and tell me what and were relay 9 is?
Thanks, Steve