I've got a 2000 S4 with 115k and every time i stop at a light or just have it idling it will stumble a little around 40 rpm up or down, but i have no CEL or any other indications of problems. ive recently done spark plugs, o2, cleaned the MAF but none of that helped. any ideas?

 

What are you scanning the car with? It might not be able to read pending codes stored. Does Your scanner have misfire detection capabilities? If so look at the misfire data when problem is occurring.
It is best to have a second person for this that can drive while someone else looks at the data.

 

I just have a regular obd 2 scanner, I used to have a misfire code but it went away after I replaced a coil pack. I think my battery is getting weak but I don't know if that would cause it

 

check compression, fuel pressure and vacuum


...not the battery