Your problem is most likely the lightened flywheel.
The engine will decellerate faster and may stall before the idle can recover. This can be cured by adding a throttle bipass that will allow exta air around the trottle when it is chopped. If that is not an option you may simply increase the idle a bit and see how it reacts.
Beautiful car by the way.
RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8