Noticed a tube disconnected from intake elbow?

[JTSVT]

As the title states....its a tube that connects to the intake tube toward the backside....I noticed it and connected it back.....but when I drove the car it felt alittle sluggish and slower....disconnected it again and it runs like a champ and noticably faster....what is this peice and why is this??....it goes along w/ some other lines......Ill take pix if necessary.....Im assuming the previous owner did this, otherwise I dont see how it would pop off???....JT

 

[ChicagoMike]

There's sensors there. You probably need it. If it runs like crap when it's connected, it's probably bad. Replace it. The sensors in that area monitor incoming air. I'm pretty sure you're not talking about the breather tube on the side of the engine head, or the IAC valve which controls idle.