SR: Super Lean 16.9+/- at idle all of a sudden?

[MrFairlady]

Been driving my car a tad more lately after it sitting for the better part of the winter.

All of a Sudden the car has been running SUPER lean 16.9 at idle only- from a Perfect 14.1-14.3 a few days ago and last few weeks when I would drive it on Short Trips.
Mods:
SR20,d/w 550cc,Sard FPR,Z32 maf,Enth Tune ECU *15psi* 93oct,GT2860BB,Walbro, Exhaust,etc - pretty basic.have AEM UEG,STRI water temp w/ adaptor in upper coolant hose.
Running 40psi base fuel pressure as per Scott@ Enthalpy

Car has Been Driving perfect Still and Boosts great (in the 11's-12) at Boost.Does not stumble or anything.
the idle worries me as its a Chip tune and nothing i can Adjust manually to Compensate.
turns out car was running REALLY hot the other day and I was actually low on coolant somehow.Never let it really overheat but did get close trying to limp it home.Put water in and filled,etc - ALL IS fine Temp wise after that.

Thats the only thing that I can say might have happened diff,and now noticing the Lean Idle.

What could it be? what should I check - Fuel Pump 1st?
fuel pressure at idle is where it should be set.Nothing changed there.