Hi guys,

I know there are a lot of threads regarding these PCV valves but I've got a question that I didn't find an answer too.

It's been mentioned that a way to test a PCV valve is to shake it vigorously and see if the valve/spring move.
I have done so on my PCV valve and it seems really loose, ie, even moving it a bit make it rattle.
Additionally there was quite a bit of oil going into the intake (over 200K km I presume) - Could this signify some issue?

I am planning on replacing the PCV valve tomorrow (if the local Mitsubishi service centre has these in stock) but I am still interested in the theory behind it.

I just called 2 Mitsubishi dealerships and they quoted me $97-$98 for the PCV valve.
Is this right?

And, are there any recommended aftermarket ones to buy?

Try the blow/suck test. It's a one way valve.
The one on my TL can rattle at idle, but tests ok.
If yours is buggered grab one from a wreckers.

If there is a lot of oil going through the hose to the intake, its not a PCV valve problem, more like blowby past the rings.
Some people install a filter to catch that oil before it hits the intake system.

I just called 2 Mitsubishi dealerships and they quoted me $97-$98 for the PCV valve.

Get a Fuelmiser one from Repco for ~$15.
Check your PCV hose and breather hoses for blockages, if you haven't already.

Thanks Max,

It seems to function properly, but I was expecting that at $20 I would just replace it. I didn't realize they were so expensive new.

As for the oil in the intake, I am not sure if it is excessive or not. The inside of the intake manifold was essentially black, but that was 200,000km worth of driving...

Thanks Max,

It seems to function properly, but I was expecting that at $20 I would just replace it. I didn't realize they were so expensive new.

As for the oil in the intake, I am not sure if it is excessive or not. The inside of the intake manifold was essentially black, but that was 200,000km worth of driving...

If it works ok, why replace it?

Most intakes get a nice coating of soot after a few years.
People are more concerned about carbon buildup in the throttle body to be honest. May be connected with rough idle if it gets too severe.
Hence a filter or catch can in the rear PCV hose to remove oil from the fumes before they get sucked into the intake before the throttle body.

Get a Fuelmiser one from Repco for ~$15.
Check your PCV hose and breather hoses for blockages, if you haven't already.

This. Seriously, Repco one is effectively identical to OEM (ok, so the colour's different) and ~$15 rather than ~$95. If the rattle & suck tests are ok it should be good*, I'd check everything else before chucking it. Simple test for PCV system is unplug fresh air hose from air inlet snorkle and pluck the PCV valve out of the valve cover grommet. With your mouth, blow down the fresh air hose. Air should flow through with a bit of resistance and should not blow through with your finger over the grommet. If it's blocked check the hoses, particularly the one from front to back covers, and replace with OEM if necessary (don't use any old hose, must be the right compound). If the hoses are ok but the system's blocked it's probably crap in the valve cover baffles. This can usually be cleaned out by removing and soaking in kero or degreaser.

As mentioned elsewhere a coating of dry soot in the plenum/manifold is pretty normal I think, if it's wet and sticky it could indicate a non-functioning PCV system or buggered rings or whatever.

* Regarding the theory, a PCV valve is a bit more tricky than a one way valve. It does protect the engine in the case of a backfire, ie. prevents hot exhaust gasses entering the crankcase, but its primary function is to meter the amount of ventilation depending on manifold vacuum. At low engine speeds the manifold vacuum is high, pulling the valve almost closed to limit the amount of ventilation air entering the combustion chambers and prevent lean running. At higher engine speeds the manifold vacuum drops and the PCV valve opens allowing greater ventilation. In other words, it's a one-way valve in one direction and a metering valve in the other. You won't be able to test the metering function with your mouth, the one-way function is testable by can suck/can't blow through the hose fitting on the valve.

Thanks guys.

I can't say I know exactly how the PCV setup works, but is it possible that a faulty PCV valve allows air into the intake manifold at idle, causing a lean mixture and hence poor idle?

Poor idle is what I am trying to fix here.
The car idles perfectly fine at times, so it is capable of it, but there is usually a choppy idle, like a slight miss

Poor idle is what I am trying to fix here.
The car idles perfectly fine at times, so it is capable of it, but there is usually a choppy idle, like a slight miss
Hi Spetz, theres a difference between 'poor idle' and 'slight miss'.
My understanding is that the 3rd gens typically have a slight choppiness in the idle.
Lots of potential causes for poor idle but otherwise the very slight hiccup that cycles irregularly is typical. I found the KL is a lot smoother at idle than the KH ever was.

I found the KL is a lot smoother at idle than the KH ever was.

Same for my TL (smooth) compared to my TJ (choppy idle).

Thanks guys.

I can't say I know exactly how the PCV setup works, but is it possible that a faulty PCV valve allows air into the intake manifold at idle, causing a lean mixture and hence poor idle?

It's normal for the PCV valve to be sucking air at idle because of the high vacuum in the intake at idle.
Pull it out of the engine at idle and see for yourself.

Idle:
High vacuum in intake = low vacuum at the rear hose due to low air speed (venturi effect). PCV sucks fumes out of the engine.

High load:
Low vacuum in intake = high vacuum at the rear hose due to high air speed through the intake (venturi effect). PCV stops sucking, fumes now go out of the engine through the rear hose into the air intake before the throttle body.

(That's my take on how the sucky-pcv-system works anyway, feel free to argue.)

Thinners is good for dissolving and cleaning out the muck that accumulates in the PCV.
Soak it for a few seconds then shake it to free up the valve. Do this a couple of times and it should free up.
Blow it out and dry it completely before refitting it as thinners can poison the oxy sensor and maybe to cat.