I will be watching your thread closely, as I am dealing with the EXACT same issue on my W124.
Idle surge for the last two years, and has gotten worse. Also sometimes stalling out when starting cold and putting in gear.
Balking on ordering the part just yet, so I will see what results you achieve...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car