Engine question

It is part of the crankcase ventilation system.

The small hose should connect to a small check valve and then on to the throttle housing. During low load conditions the low pressure in the throttle housing is used to evacuate gasses from the engine through this hose. The check valve will close when there is pressure in the throttle housing (when the turbo is providing pressure).

The large hose should connect to the suction side of the turbo and is used to evacuate gasses from the engine when the turbo is providing pressure.

This is an overview. The details vary between engine models.

A working crankcase ventilation system is vital for the engine.

A common problem. Just buy a new rubber ring.

Yes. You didn't tell us what engine this is, but the idle will be affected if the crankcase ventilation system is leaking. The leak will provide extra air into the throttle housing and the ECU has compensated for this by closing the idle control valve (older engines) or throttle plate (Trionic 7 engines). When you fixed the leak the ECU had to find out what to change to get the correct idle again.

In message , Johannes H Andersen writes

Which engine? PCV valve?

Does this apply the same to non-turbos? I have the hose running to the throttle housing but there is no check valve. How vital is it to have one?

-- Christian

No. The check valve is only required if the pressure in the air intake will increase above atmospheric. This can only happen with a turbo charged or supercharged engine. On a NA engine, the pressure will always be lower than atmospheric pressure.

Except when it backfires through the carb.... That's why there's a check valve in the PCV system on the V4 engines.

-- MH '72 97 '77 96 '78 95 '79 96 '87 900T8

No. The goal is to locate a source of low pressure. For slow cars this is somewhere on the throttle housing. For fast cars you need two sources, somewhere on the throttle housing when the turbo is not providing boost and just before the turbo when the turbo is providing boost.

The check valve is only needed on turbo cars.

If the check valve is broken or missing the turbo will pressurise the crankcase. This is bad, very bad.

I believe engine is B202S for MY 1993 9000 CSE 2.0 LPT