the tickover was a bit lumpy, and like a fool, i turned the wrong thing, underneeth the inlet manifold, theres a spring surrounding a plug that you can turn. Firstly what is this plug? and secondly, can someone advise whats needed to be done if this is changed? is it just air, cuz the car runs fine, if not slightly quicker, but is this going to damage the engine, ive sorted the tickover now only slightly lumpy, but its how its allways been.

Help needed guys!!!! thanks!