It's called "Auto choke" in desi terms, and was malfunctioning in my case. So i bypassed it altogether.
In your case, if idle RPMs are OK, then don't fiddle with it.
Btw, one of my colleagues claims 15-16kpl from his Civic 2005 MT. He went to some area near to Multan along with a colleague having Euro 2 Mehran. The civic consumed 34L, while Mehran consumed 33L.
But he's the only one praising the fuel avg. of his Civic. Everyone else is crying