Subaru - Outback :: Rough Idle And Lots Of Vibration After A Timing Belt Change

My wife and I recently bought a 2005 Subaru Outback 2.5 XT with an automatic transmission. Last week, we had the timing belt changed by a mechanic I've gone to for the past four years and trust a great deal. He changed the timing belt, drive belts, water pump, pulleys, tensioner and a few hoses, and everything seemed to go off without a hitch. After picking up the car, though, we noticed that the idle seemed much rougher than it had in the past. We can't tell if it's also rough during driving, or when the car is in park or neutral, but there is definitely considerably more vibration when the car is stopped in drive and idling--you can feel it throughout the car. I haven't noticed it until the car has warmed up.

I asked my brother, who is a mechanic in another state, if he had any thoughts, and he said it could be that the belt is off a notch, a vacuum leak or an unplugged sensor. I brought the car back to the mechanic today to see if it he could fix it, and he said that the CEL would be on if it was a vacuum leak or unplugged sensor, and that the car has an automatic idle that the belt change would not have adjusted. He asked if the vibration was getting any better, since when the battery was unplugged it would take the computer awhile to relearn the correct idle, but we've driven it a few hundred miles and it hasn't gotten any better. I left the car with him to take a look at it, but he just called and said he couldn't find anything wrong.

I want to chalk this up to us imagining something, but we both have no doubt that there has been considerably more vibration at least when the car is idling since we picked it up after the timing belt change. Is there anything else that it could be or that I should ask my mechanic?