Running lean at idle

[Desperado]

My car idles around 1100, and is smooth not jumpy. However 9 times out of 10 when idling the wb is showing around 16.9, but if I'm driving steady it goes to the 14 - 15 range and 12s for wot. When I do a vacuum pressure test it seem to have a small leak around the screw of the TB but that's about it. What else could cause this and how serious is it scenes it doesn't have a load on it? Honestly if I didn't have a wide band on it I wouldn't have noticed.

[KeithMac]

Have you got a Blow Off Valve?, probably open slightly at idle sucking unmetered air into the engine..

It's lean but if you have no stalling issues it's not the end of the world. As long as you are not overheating at idle it won't damage the engine.

[Desperado]

Yeah I run open atmosphere with a blitz. No over heating or anything bad, just me being paranoid. Thanks