2000 jetta loose hose? fuel injector?
 

Hi... A month or so ago I was driving downtown and at red lights the car was "shaking" as if the rpm was too low, then the catalytic converter light/telltale sulphur smell emerged and it was really sputtering on the way home.... took it to my boyfriend's dad's shop who said it was just a loose vacuum hose, fixed it, and it was fine.

Well, two days ago I was driving home and the exact same thing happened. I took it to the same shop. They said one of the cylinders wasn't firing because of the fuel injector. They sent the fuel injector to a shop, and were told nothing was wrong with it. They reinstalled the fuel injector and now it runs fine. (?) They have "no idea" what could be wrong. (I paid $250 for that) Anyone have any idea what the problem is?

Thanks! -Meghan