I have a theory

[xavier]

A Few weeks back when I was sorting my exhaust manifold my son removed the breather pipe on my 323i. I popped a little breather filter on the rocker cover where the pipe had been removed. Now I have a catastrophic oil leak. I think the filter has blocked and the head pressure has gone mental. Does anyone agree? The little filter is off and I will get some more pipe and plumb it back the way it was before.

[harry_p]

The standard breather system works fine, it doesn't need messing with. As well as oil leaks and open breather system on an e30 can also make it idle and run badly.

[Brianmoooore]

If you've left the pipe open on the inlet manifold side, then the engine will definitely run badly, to the point of possibly damaging pistons.
The M20 was designed to have positive crankcase ventilation, and removing the pipe and replacing it with a filter will cost you a small, but measurable amount of power.
If the car's pumping oil out of the open pipe on the rocker cover, then it suggests your piston rings are way past their best, although a build up of sludge in the labyrinth under the rocker cover will also cause oil to blow out.

[xavier]

OK. So I will pull out the breather filter and reconcect the piping. As my son did the removal of the piping, and the original pipe was thrown away and do not have much of a guide. I am assuming I just need to get a suitable diameter of breather hose to connect between the throtle body and the rocker cover breather outlet. Correct me if I am wrong, but there is NO valve between these two points?

[kam-325i]

No Valve.