83 380 sel - strange idle behavoir
 

For the first start of the day my 1983 380 sel idles perfectly for about 2 seconds, then the rpm's drop way down and the engine struggles to stay running, sometimes stalling, but it will restart instantly.

Here's the weird part, after 60 seconds the idle will smooth out and be perfectly normal for the rest of the day, as long as the engine doesn't get completely cold. The behavoir is absolutely predictable, it's always exactly the same.

I cleaned the idle control valve (it was very dirty) and replace the rubber parts it attaches to, but it made no difference. I also replaced it with another cleaned one from the boneyard, and it made no difference.

Can anyone give me an idea of what part is at fault?

cold stasrt valve?
warm up reg

if its ok rest of day
must be something w cold start..

just my guess