[a1f6d]

I've got a question about the PCV system on a 1990 900S. Looking at the black plastic nipple that is installed in the valve cover, there are two barbed hose attachment points. One is large and has a hose that runs to the throttle body upstream of the throttle plate. The other is small and has a small vacuum line that runs to a port on top of the intake manifold. The passage from the large hose through the plastic nipple into the valve cover is completely unrestricted and allows air to flow easily in either direction. However, the small passage does not appear to allow any airflow through it at all in either direction. It seems to be nothing more than a fancy plug in the end of the vacuum line from the intake manifold. I assume air is supposed to be able to move from the valve cover to the intake manifold through this vacuum line (regulated by the in-line PCV valve). Any thoughts on drilling this passage through? Not sure if I'm misunderstanding the system or just got a bad part.

 

[Artfulkatana]

Isn't there a small check valve on the 3/16th vacuum line going to the manifold?

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[a1f6d]

Yes, that's the in-line valve I mentioned. I don't think this system has ever been set up properly in the time that I've owned the car and I'm trying to put it all right. There doesn't seem to be much clear info on it though.

 

[Rodentmaster]

Yes - in NA form, the small tap of valve cover breather should be open to crank case/valve cover air flow - no restrictions.
Either the small tap has been blocked by a previous owner or become blocked from long term carbon or oil sludge build up.
When the throttle body is correctly aligned and idle valve is working correctly, the hose from the breather to the manifold is an integeral part of the idle air flow balance. What you might discover when the breather is cleaned out, is that the idle will be higher. If so, this may be or might have been due to the throttle idle stop being having been adjusted to compensate for the air breather slowly fouling up.

edit......in NA form, there should be NO valve of any type in the hose between the valve cover breather and the manifold.

 

[Jim Mesthene]

Every car (USA anyway) has an accurate vacuum diagram on the sticker next to the fusebox.

 

[peva]

Every car (USA anyway) has an accurate vacuum diagram on the sticker next to the fusebox.

US only. Don't have it in Europe. Not a bad idea anyway. Though most idiots wouldn't read it anyway before screwing the car up.