Consider yourself lucky. I have a mild cam...only the E-303....and I get random surging, except mine, if left to do it, will go from mild to severe surging and then choke and stall. I hear it's a problem with the IAB valve design being too restrictive. I think you can order a part from Ford that fits in between the IAB valve and has a screw on it that you can turn to let in extra air. I guess it works, but I've yet to try it.
But try cleaning the valve anyways, just to see what happens. Oh and I noticed you call it an "IAC" valve, instead of "IAB".....didnt use to own a GM by any chance did ya? 
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'91 Mustang GT 5.0 AOD Daily Driver
Current stats: NEW 302 short block, E-303 cam (@.050, 220/220, .498/.498, 110 degrees), 1.6 roller rockers, Performer RPM heads (aluminum, 1.9/1.6, 60cc chambers), Cobra intake, Granatelli 75mm MAF, Billet AFPR, Equal-Length Shorty Headers, Off-Road X Pipe, Flowmasters, 4.10 POSI
13.73 at 103.8, ~2.2 60'
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