This may be a stupid suggestion, but are you sure the MAF is facing the right way? I had an Altima and many people that installed the intake accidentally put the MAF in backwards, and it would do exactly what you described. In that case it was pretty easy to accidentally reverse it. Not sure about the Simota, but on the AFE the screw holes for the MAF were offset IIRC to help with proper alignment. Just a suggestion.
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