I have a newly rebuilt 355 LT4 in a 96 vette and I am expierencing a surging idle but only in open loop situations as soon as it enters a closed loop the surging stops and idle stabilizes.

Mods include:
hotcam
ported heads
52mm TB
EM long tubes
30# injectors
air pump delete
cat delete
mezeirie water pump
corsa exhaust
ED Wright reprogram

Strange scan data @ idle:

OPEN LOOP:--------CLOSED LOOP:
Map 27 in/hg --------14in/hg
IAC 122 steps --------50 steps
timing 25* -----------27*
cell 16 --------------16

Any ideas on what to look for in rooting out this problem?