P0506 Idle Air Ctrl Sys and Failed smog test

[Homeoboxter]

Dear All,

I hooked up my code reader which revealed the following code: P0506, idle air control system failure. The engine has a stable idle when cold, ~800, when it warms up it goes a bit over 1000 and fluctuates between ~1100-1200. I`ll look into this tomorrow but I thought I ask the Community first if there`s anything obvious to look at with these symptoms. Intake plenums and throttle housing are cleaned, the whole engine has just been freshly put together.

Not sure if related, but the car failed the smog test yesterday. Emission is fine, I was told the reader could not reveal the fault code history because the battery was disconnected for too long, for 13 years actually. So I was told to put a couple hundred miles into the car and go back and it would pass...

Thanks for any insight.