hardtop

I have an 03 A6 2.7T. In gear and at an idle (like sitting at a stop light) the car will drop 200-300 rpm and then come back up. It last like a split second. I have taken it to the dealership three times now and they can't figure it out. It isn't throwing any fault codes. Have any of you have a similar experience? Any suggestions would be greatly appreciated. This is driving me crazy.

quickaudi:STFA

don't tips have a secondary air injection system? that have anything to do with it?

S4_Cinci (I S'edTFA)

issues as rough idle or surging. May not be a large leak - listen for any hissing or sucking sounds. Look for any cracks in the vac lines - the ones with the woven sheaths are well know for crumbling underneath this woven sheath and the leak is hidden.

You don't have a lot of age on the car, but a line could be just loose at a connection. Also be sure that you don't have any corrosion on your battery terminals or a bad main ground (body ground). This can cause issues and that is something so basic that many techs overlook it, esp on a newer car. Always start with the basics. If you can jiggle the vac lines SAFELY with the engine running, this is a good way to see if a noise changes or appears/disappears when you move a certain hose or if the idle speed changes when a hose is wiggled.