D15b vtec 3 engine unstable idling?

help!!! experienced unstable idling of my d15b stage 3 vtec engine, also, had a feeling that most of the time my exhaust (simota air filter) is not functioning...noticed that other engines of the same specs eh malakas ang higop ng hangin once buhay ang engine, yung sakin wala...any advise would be of great help mga sir...thanks