Vacuum tube?

Okay, i have a 1992 corolla 4A-FE and i have replaced the stock air filter in my corolla and i took off the whole assembly.but now there is a a open pipe that was hooked up to the filter. it is a kind of vacuum hose. When it dont cover it, it has a high idle, but when i cover it, it idles really low. Does anybody know what this tube is?It was hooked up to the bottom of the tubes.