hmm... check all your vac lines like said above, but i was just thinking...

If you get a plastic bag and cut it up and wrap it around the the TB and tape it down good to create the best seal you can then start the car and give the engine a rev to see if the bag gets pulled in as if the air is being sucked out?

I dunno if that would work, but it just seemed like an idea to test the seal around the TB without removing it.