ok i know i saw thispost somewhere before and i cant seem to find it. because now i have the same problem. when i start the car it starts to make this loud vacuum sound. and now the check engine light comes on. anyone with any ideas what this is and the guy who had this before can you tell me is this something i have to put a large sum of change to fix. i have a a4 b6....i would not posted if i had found that older post but the search option seems to be retarted at the moment. thanks if you can find some info to let me know.

 

Have you scanned it for codes? I don't know but that vacuum noise might be your secondary air pump? Do the B6's have this? I know mine doesn't so i have no idea what it sounds like but it's just a guess. Get it scanned and post the codes.

Josh

 

Air injection pump look for disconnected pipe lines or crack in the pump itself. It will be located on the pasengerside towards the front. Easist to get to from under the car