What is this??????
 

Its a rubber boot that covers a plug and it pulls vacuum. Its located between the 2nd and 3rd spark plug on a 2.3l. I keep putting the cover back on but every time we drive it pops out and it gets terrible gas mileage. please help

Well, what is it? I assume tribute. Take an image, and post it. It could be map sensor, fuel pressure regulator. What part of the world is it located?

It's a 2008 Mazda tribute withe the 2.3l. I think I have it narrowed down to a
Cylinder head temperature sensor. But I would like to hear other opinions. I don't have any lights or codes. Gas mileage just sucks bad. It's on top of the motor between the 2nd and 3rd spark plug. It's like a rubber plug that snaps in and underneath is the cylinder head temperature sensor. The rubber plugs keeps popping out causing a vacuum leak.