Is there some sort of catch on the opposite side of the IAC plug that I'm not squeezing properly?

 

Did you pull back the rubber boot ?, I know it is tricky to get loose if you squeeze over the rubber boot, but if you pull the boot off the plug then it is an easy squeeze and it should come loose like any other clip.

 

that plug is a b**** to take off. it was hard to take off the first time for me as well. just gotta keep trying and wiggle it off

 

The clip release button is on the bottom. Feel for it through the rubber cover.