2005 xA getting a P0505 Idle Control System code, first a pending code soon after resetting codes, then CEL on next restart. I can't get the OBD monitors to "ready" without this code returning every time I try.
Startup from cold, it idles very low at first, then establishes a stable idle within a few seconds.
I have read several threads here on this and seems like the throttle body is the most likely cause?

 

If it runs normally during driving, it may be that the idle air controller has carboned up... this happens
The electrical connection to it could be the issue too - corrosion can build up easily with a car this old
This video describes where the part is.

Try unplugging it, put some contact cleaner in there and wiggle plug in and out a few times - perhaps that will fix it.
Much harder is taking it apart and cleaning out some carbon that seems to accumulate.

 

Thanks. I should probably add that I'm in no way mechanically inclined, and just researching a little so I have a little bit more knowledge on it for when I eventually have it worked on by a qualified tech.
It does seem to run normally when driving. I checked the idle speeds today using OBD (BlueDriver) and cold it idles around 900 RPM, and warm it's higher, around 1200 RPM, so just the opposite of what it's supposed to do, right?

 

Fixed. It was the idle control valve. Had that replaced, and throttle body cleaned out, and it stopped throwing that code and passed smog inspection. Idles a lot smoother and quieter now.