I'm buying an s5 t2 today. It has 30k on a rebuilt with lots of paperwork. It has a rough idle. What can be causing it. He told me he got a compression test done with an actual tester and it read 90s all across the board. I haven't done a test myself. I know how to do it with a regular pressure guage. The funny thing is that. It's only rough at low idle up until 2k rpm. After that it's all good. It has lots of power. Has anyone experianced this? Any info would b great thankS!!!

 

It could be a lot of things. Do a thorough search, and you will find some info.

 

Look for a leaking vacuum hose or a leak in the intake piping. Either one can result in a rough idle.

 

The owner said it might be a leaky fuel injecter cause it's also running a little rich.