Audi Repair Questions? Ask a Mechanic for Answers ASAP
What engine do you have? it looks like you have a vacuum leak, not only the misfires at idle, but the fault for a "brake booster vacuum system mechanical failure". You should be able to hear the hissing if you listen in the engine bay with the engine running. Roll the vacuum lines and other vacuum hoses between your fingers to feel for cracking or flattened hoses.
Because of a few different reasons- at idle, the intake manifold vacuum is at it's highest, so any air leak is going to be sucking strongest at that time. Also, at idle your throttle body is closed pretty far down, so any amount of "unmetered" air in the system is going to be pretty large compared to the amount coming through that tiny throttle body gap.
The 1.8T has some common vacuum leak points- if you take a look at the valve cover, there is a rubber "Y" pipe at the end of it, check that and then follow that to the plastic curved pipe below it which often cracks right below the rubber pipe. Also, on the underside of the intake manifold, there are a couple of vacuum fittings with half inch lines- they often crack there.
That Y pipe at the end of the valve cover is part of the PCV system. It runs down to a one-way valve below the intake at the front of the block, and directs to a couple different hoses. The hoses break more commonly than the valve, but if I find anything broken in there I usually replace all the hoses and the valve (as trying to take any of it apart usually breaks it anyway)