BMW cold idle issue

[Pronto]

My Brother-in-law bought a used 2000 BMW 535I from a friend of his. It's in very good shape and was well cared for. It is experiencing a cold rough idle issue but not throwing a code. When it is first started cold overnight it has a good smooth high idle. After a few moments the idle will slowly drop down some as expected but then it starts to get a rough idle. It will be choppy and die if the idle is not kept up to about 1500 rpm. The temp gauge has a blue area on it in the cold side. Until the needle goes past the blue area the car will behave like this. Once past the temp the car will idle fine and restart fine. He can even restart it several hours later with no problem. This has happened in both cold and warm overnight temps but only if it's sat for more than 10+ hours. Other than that it seems to run fine. He has a professional mechanic friend that cleaned the throttle body the other day but didn't fix the issue. It's difficult to show unless the car is left overnight which I witnessed yesterday. I didn't have a scan tool to check at what temp the engine will idle correctly but the issue seems to be tied to the temps between cold and a certain point before it gets to normal operating temp. I did a quick visual scan of the vacuum lines and they they seemed in good shape and tight. I think it might have something to do with a temp sensor or the thermostat. Any ideas on this issue? Thanks.

 

[notacarlo]

Check to see if there's a service bulletin on that car. There may be an update for the cold start fuel map. Not uncommon.

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[Pronto]

Ok

 

[Pronto]

After doing some research it looks like it may be a seal leak in what they call the double vanos. Some kind of variable timing item. Looks like some O rings need to be replaced.