What engine are we working with?

 

1.2 petrol 5 speed manual transmission.

Issues.
1. Hissing sound only when turn off from engine running. But no sound during engine running.

2. On start, rpm is normal. But overtime when the car is being used like for 10 minutes or longer, rpm drops and stay low when idle.

3. When changing gear either from high to low or vice versa with gas pedal fully released and the clutch fully depressed, the rpm revs high. This revs is very very noticeable even from 4 gear to 5. Before it was not like this.

All fluids, battery, oils etc etc are fine and perfect.

Please kindly refer to the link for more clear description...

https://youtu.be/SfsBP1XfKZw

 

If the noise is gone with the hose blocked the noise isn't likely to be anything to do with the hose.
So that would seem to suggest it's the valve but I've never heard one making a noise like that before.

 

So I would replace the pcv valve to remove the noise???

I guess air cannot be sucked out properly from engine through pcv valve by the pcv hose since the pcv valve is not functioning well... blocked or clogged etc???

 

So I would replace the pcv valve to remove the noise???

Yeah, try replacing it and see what happens.

With the hose plugged with a bolt does that cure the engine speed issues?

 

Sir, one idea before replacing the pcv valve.

Started the engine, and took off the engine cap and left open, the pcv valve and hose are attached too. Now, I off the engine, however, still the sound exists with "engine cap removed".

To my understanding, the sound is made by the air "blowby gas" within the piston which travels to pcv hose through the pcv valve. So, this gas now must come out to the open cap and make no sound anymore. But, when left opened, still the sound persists.

Please correct the above ideas ?

 

To my understanding, the sound is made by the air "blowby gas" within the piston which travels to pcv hose through the pcv valve.

From what you described, the sound is actually being made when the manifold vacuum that is acting on the valve is removed (engine switched off). I don't think the sound has anything to do with "blowby gas" or the pressure in the crankcase. You could connect a vacuum pump to the valve and pull/release vacuum with the engine off to confirm, or just use the money you'd need to spend buying a vacuum pump to buy a new valve and confirm valve failure by substitution of the part.

 

Remove the pcv line from the engine. Started the engine, and the valve is sucking my thumb, and I off the engine. At this point, the same hissing sound still arises which was the same case when the pcv system is connected to the engine. The sound comes only at this pcv connection and not from engine compartment.

Following were tested which every one confirm ok.
1. Pcv valve is sucking when block by thumb. This is ok.
2. The hose also is sucking when block by thumb. This is ok.
3. The pcv valve give a knocking sound when shaking independently. This is ok.

And air passage is blocked when it is blow through the smaller hose of the pcv valve but comes out when blow through opposite hose of the valve. This too is ok.


From the above practical test, is it pcv valve failure? But I think it's very unlikely that it is failing coz it seems all practical test are ok.

 

From the above practical test, is it pcv valve failure?

It sounds like the valve is functioning correctly, but you have also confirmed that the unusual sound you hear when shutting down the engine is coming from the valve. You asked what was causing the hissing sound and now you know.

Also, for the rpm issues, I disconnected the iscv and started the engine. The rpm immediately rises to 1to1.1k rpm and when reinsert back, it drops to around 8k again which is the same case as was before.

The reason I suggested disconnecting the ISC actuator was to see if that is where the hissing sound was coming from. You've already figured out where the sound was coming from so there wasn't any need to disconnect it now.

 

Also, for the rpm issues, I disconnected the iscv and started the engine. The rpm immediately rises to 1to1.1k rpm and when reinsert back, it drops to around 8k again which is the same case as was before.

 

How to clean the pcv valve???

 

I don't know the specifics of how the idle control valve on your particular engine works. Is it a needle valve? I have no idea.
Generally the more an idle control valve opens the higher the idle speed will be, so I doubt it would be fully open during normal warm engine idle.

 

Screen shot of the obd data with engine off. Hope this might help in solving low rpm issues.

 

Another screen shot when engine is running.....ie idle

 

But many times I'm confused how pcv valve is positioned....see picture attached herewith for example.

The gases are not supposed to touch with oils .....but....in present case, it seems gases are coming under the top engine cover where oil spill and scattered all throughout the camshaft etc etc

 

see picture attached herewith for example.

Your picture is a little over simplified. The PCV valve doesn't just pass through the rocker cover into the inside of the engine where all the oil is. It passes into an oil separator chamber that is designed to separate the liquid oil and the gases, although some oil vapour is always drawn through the PCV valve.