...valve) and the intake manifold inner surfaces and so on. Just about every place, surface that the intake air comes in contact with and then every surface the exhaust gases contact will have an oily film (or worse).
Even with some clealing of the TB and the cleaning of the manifold area where the AOS hose connects to the intake manifold and as far into the manifold as one can reach, there is quite a bit of intake and engine surface area that can accumulate some oil film.
It takes time for this oil to be reduced by air flowing past it and by the combustion process and the heat of the exhaust to burn away all of this. The oil doesn't evaporate, is not thinned by any contact with gasoline (at least upstream of the injectors) so all you have is gravity and air flow. In cooler weather of course the oil's going to be less fluid and thus some oil can remain for a long time.
Upon a high speed shift from say 2nd to 3rd there is a tremendous amount of air flowing through the intake and during this period some oil can be dragged along and into the combustion chambers and sometimes a bit of smoke will appear at the exhaust.
Whenever an AOS goes bad and after it is replaced I like to -- though I haven't always done it -- run at least a bottle or two of Techron through the engine as per directions on the bottle to at least ensure the fuel system and injectors are clean and some valve, combustion chamber, exhaust system deposits are removed.
The new AOS is not perfect either. It can allow under some conditions some oil vapor to make its way through the AOS and into the intake system. Some engines generate a bit more blowby (even though they still run good) so an AOS in one engine can have more work to do that one in an engine that generates less blowby. Also, engines can differ in their valve stem seal performance and a bit of oil smoke at various times is the result.
Plus the type of oil you use in the engine, how many miles it has on it. The more miles means more contamination and dilution with fuel and water and this oil then is more prone to generating oil vapor (the oil aerates more readily than fresh oil).
Next some engines are more sensitive to the oil level too. I have come across some S owners who have found oil smoking on the track to be reduced if they run the engine with the oil down a bit from full (when measured hot). However, at one S driver reported that to avoid the flicker of an oil warning light he had to run his Boxster engine with its oil level a bit overfull.
Might point out that Porsche really doesn't support these engines on the track. They are just not up to it, though there are many owners who track these cars and experience no problems. But because the way the engine is designed it is just not able to scavage oil adequately under track conditions and oil smoke once in a while is going to happen. And this activity will put no little amount of oil on the intake manifold surfaces (and other surfaces which I covered above) and even after one has left the track and is driving on the street under some conditions oil smoke has to be expected.
Sincerely,
MarcW.