AFAIK, this is the portion of The Moose that Ford attempted to fix by issuing TSB #97-22-3 (applies to SVTs - older models have a different TSB#). This TSB replaced the bagpipe/bellows ass'y from the intake hose to the IAC and also the IAC itself. It attempted to fix the A/C compressor-related surge accompanied by The Moose. As we all know, it quieted the Moose, but did nothing for the compressor surge.
However, there's also "another Moose," which seems to be unrelated to either the IAC or the A/C compressor. It occurs mostly in cold engines in cold ambient temps, and may or may not have any effect on RPM.
FWIW, my engine has the "updated" IAC and tube, and surges when the compressor kicks on. Also, it has the "other Moose" in cold temps.
At this point, your guess is as good as mine. Two problems to solve, both related to intake resonance. Happy hunting.
