Hey guys! So I just brought my GTI back from an oil change and right off the bat I noticed that there is a bumping sound when it is idling, but can't be heard when I give it gas. Along with it the cars RPM's seem out of whack. Say I'm switching from 2nd to neutral at 2500, the RPM's will stay at 2500 for a second before going back down to 1000. Once it comes back down it will go back and forth between 1000 to 1100 revs. I thought it was a vacuum leak at first, but it wasn't having the problem before the oil change, so I almost think it has something to do with that or they just messed something up with the engine whilst in there. Any help is greatly appreciated, thanks!