P0505 and FIAV question

[culiced]

Heres the deal, about a month and half ago my car had idle surge only when its cold, but when it was warmed up, it idled fine. There was no CEL. After looking stuff up, came to the conclusion that it was the FIAV. I never fixed it. Last week, My CEL came on and it was P0505, Idle control system malfunction. Now, my idle when warmed up is around 1K. I checked the resistance in the ISC and they were all 29.5, give or take so it seemed fine. Could the FIAV cause the cel to go on? Because now I have idle surge when cold and then settle around 1k when warmed up. Am i missing somthing? any pointers would be appreciated.(I just drove it today after checking the ISC and now it seems worse. after i stop to a red light, the rpm goes to 1400 first then settle around 1K, does this mean the ISC is bad?)

Im about to buy the FIAV block off plate, this should help with the surge on cold start right?

thanks!