IAC failure?
 

I had been battling this rough idle issue for a long long time. It went through several shops. No one could point a finger at anything. I took it to a friend of my dad who has been a tech for 35 plus years and he said it needed decarbonizing and that was it. He did that and it seemed fine but he had said that somtimes that stuff wipes out the IAC valves. Is this true? I have been driving it for lke 500 plus miles and it was running amazingly. All of a sudden I started it up warm and it was idle up and down and up and down. So I got out and tapped on the iac housing with a scewdriver and it went back to normal. Does this ussually mean that you need an IAC. I pulled it out and checked for carbon and it was clean as a wistle. let me know what you guys think. Maybe it just needs to be reset?

Is Decarbonizing the same as Seafoaming it?

same type of thing but my mechanic used BG industion system cleaner.

Your problem seems to be very similar to mine. A while back I sea foamed my engine and not long after that the idle starting acting erratic. Never really got around to checking it out and its still does it ever so often. I'll have to look into it a little deeper but your friends dad may have hit the nail on the head with this one. Let us know what you find.