GT-40 pulsating idle

Have a 2000 SN with GT-40. Idle pulsates from 550-950 rpm about every second or 2. Runs great under power. I read all posts and replaced the IAC with a new one. No difference. Checked all connections, all plugs, reset large computer plug, no difference. I noticed when I took off the IAC , there are two large holes in the throttle body that matches up to the holes in the IAC. There is a mesh screen in one of the those holes. Could that be clogged up? Any help would be greatly appreciated. This is driving me nuts.