I have a manual 2000 Passat, engine code ATW, that started acting funny out of the blue (sort of). A bunch of youngins were driving on the road next to me and started revving their engine, so I revved back. Nothing prolonged, just a quick double rev... vruuummmm VRUUUUUUUUMMMMMMMMMMM. Something like that. Immediately afterwards, my car started running rough, not sputtering, just vibrating like something is off balance. If you put your hand on the shifter, you can feel the vibrations very well, but in general it feels fairly shaky just sitting in the car. I also have a little less power. The vibration stays no matter how fast you go, but tends to dampen a little when on the highway. The tricky thing is that there are no trouble codes being thrown. My thought is maybe a vacuum hose popped off during the revving, but I don't see any visible lines hanging. I took it to my mechanic, who is usually extremely good at troubleshooting, wasn't able to figure it out (didn't charge me either but I gave him something for his time). Any ideas what this could be?