Lean Idle After New Exhaust???
 

So today I took the boosted tC to my exhaust guy to get new exhaust put on it - the old exhaust rattled like hell at low RPM.

Old Exhaust
Fabricated 3" all the way back behind the axle.
Flowmaster 2 chamber muffler
Resonator
No catalytic converter

New Exhaust
Fabricated 3" exhaust dumped before the axle.
No muffler
No resonator
No catalytic converter

After starting up the car with the new exhaust I immediately noticed much leaner AFR at idle on the monitor (17.9-18.0, sometimes out of range of the monitor). The car does not sound or feel any different at idle - about the same as before, perhaps maybe even slightly smoother. This worries me however, as I don't want to burn up any valves or anything else with a super lean idle. Here's the kicker though, during driving and while in boost AFRs are the SAME as they were before the new exhaust was put on and the car runs somewhat stronger on the high end. Any idea what the hell is going on or am I just absolutely going to have to get this car retuned at idle and will I hurt this car by continuing to drive it like this?

First anytime you change something you should retune.
Next since you went exhaustless you run a bit lean on the gauge. Due to the outside air flowing in the pipe and throwing off the readings. Where is the wb mounted?

with new exhause the car has less back pressure, all you need is a tune to get your afr back to normal.