Erratic Idle

[sambo]

Alan have you changed the PCV valve since remapping etc? There prone to failure after power increase and can cause idle issues like you have.

Huh . . . please explain how a remap can affect the PCV?  Or do you mean the DV? 

Mine was caused by the DV but you have the forge one, i know they require servicing but not sure what needs to be serviced? May be worth a look?

If the DV is on its way out, then it would usually be much more bothersome during high levels of boost.  Again, I can't see how a u/s DV can cause erratic idling! 

Hi TT.

PCV valve is prone to failure after a remap, i'll dig out some info in 2 min's over on 'the other site'

The DV is also an odd one, which neither me, or my mate who is a (decent) VW master tech could figure out the logic behind, but I can assure you 100% it does effect the idle as mine did (an someone else on this site) when I first bought the car. Would love an explaination as to why/how but after changing it everything ran sweet as a nut!?

Sam

[sambo]

Just had a quick scout around but couldn't find anything worth posting, but basically would it be fair to say that if the PCV valve is obviously under positive pressure (boost?) then remapping will increase this pressure and lead to premature failure of the diaphagm?

Would that make sense TT?

Sam

[AlanD]

Id like to think my Forge DV isnt at fault. It went in a few days after the remap which was in December so only 8 months ago . . . . .

I'll see what VAGCOM says on Wednesday and update.

[ub7rm]

Going back to the mk4 days, when I had a dodgy idle the first time it was the MAF (remember it doesn't always cause a fault code, you have to log it [or disconnect it] to see if its bad) and the second time it was a lambda (O2) sensor.  The other mk4 favourite was the temp sender but I've not heard of this being an issue with the mk5...

Its annoying when stuff like that happens 

[Teutonic_Tamer]

Just had a quick scout around but couldn't find anything worth posting, but basically would it be fair to say that if the PCV valve is obviously under positive pressure (boost?) then remapping will increase this pressure and lead to premature failure of the diaphagm?

Would that make sense TT?

Sam

The PCV valve has NOTHING to do with turbo boost!    It is ONLY the DV which is affected by turbo boost, unless you have modified your engine to work on the two stroke cycle!

[sambo]

No idea then, you know better than me, but it is all the talk over on the 'other' forum about remapped car's PCV valve's failing and what is the best way to upgrade to prevent carbon deposits building up on the valves.    Presumably the more power you run the more pressure you have in the crankcase? You tell me as i'm not a technician!! 

[Teutonic_Tamer]

No idea then, you know better than me, but it is all the talk over on the 'other' forum about remapped car's PCV valve's failing

So just 'cause someone on another forum got it wrong, but everyone agreed like a following flock of sheep - then that makes it 'correct' then?! 

Which 'other' forum was this?

and what is the best way to upgrade to prevent carbon deposits building up on the valves.   

Ahhhh, that is a completely different issue - but has nothing to do with remaps or turbo boost - or any other similar 'off-tangent' hair-brain ideas!

Presumably the more power you run the more pressure you have in the crankcase? You tell me as i'm not a technician!! 

Pressure in the crankcase has nothing to do with the turbo boost, nor 'power'.  I suggest you go to a library and read some propper textbooks. 

[ukdub]

Just had a quick scout around but couldn't find anything worth posting, but basically would it be fair to say that if the PCV valve is obviously under positive pressure (boost?) then remapping will increase this pressure and lead to premature failure of the diaphagm?

Would that make sense TT?

Sam

The PCV valve has NOTHING to do with turbo boost!    It is ONLY the DV which is affected by turbo boost, unless you have modified your engine to work on the two stroke cycle!

The PCV valve may have nothing to do with boost,  but it can be affected by it.  Therefore increased boost can damage it.

Crankcase Ventilation

The crankcase is maintained in a constant
vacuum while the engine is running.
The crankcase breather that supplies
this vacuum is connected to the intake
manifold.
The crankcase blow-by gases are separated
in two stages. In the first stage, the
primary oil separator in the oil filter module
takes most of the oil out of the gases. A
second separator in the cylinder head cover
removes the remainder of the oil from the
gases.
Since a turbo engine requires a more
sophisticated pressure control system, a
two-stage pressure control valve is located
on the cylinder head cover. If vacuum exists
in the intake manifold, blow-by gases flow
directly into the intake manifold.
If a boost pressure is present in the intake
manifold, a one-way valve in the pressure
control valve housing closes and the blowby
gases flow into the cylinder head cover
ahead of the turbocharger. The system can
detect faulty installation of the pressure
control valve. Unmetered air is detected by
the reaction of the oxygen sensor.

[sambo]

No idea then, you know better than me, but it is all the talk over on the 'other' forum about remapped car's PCV valve's failing

So just 'cause someone on another forum got it wrong, but everyone agreed like a following flock of sheep - then that makes it 'correct' then?! 

Which 'other' forum was this?

and what is the best way to upgrade to prevent carbon deposits building up on the valves.   

Ahhhh, that is a completely different issue - but has nothing to do with remaps or turbo boost - or any other similar 'off-tangent' hair-brain ideas!

Presumably the more power you run the more pressure you have in the crankcase? You tell me as i'm not a technician!! 

Pressure in the crankcase has nothing to do with the turbo boost, nor 'power'.  I suggest you go to a library and read some propper textbooks. 

You seem rather belligerent T_T  for someone whom people are asking your expert opinion about something which appears to be your profession?  I am not a mechanic/technician/workshop monkey so my above suggestions were purely speculative based on a number of GTi owner's having the same problem with a particular component. Far to co-incidental for me.

Maybe an understandable reply to us mere mortal's about exactly why this could be of no relevance to said problem, would be a little more useful to the topic, rather than shoot anyone down in flames on the basis you have a far superior wealth of knowledge!

Sam

[Teutonic_Tamer]

Just had a quick scout around but couldn't find anything worth posting, but basically would it be fair to say that if the PCV valve is obviously under positive pressure (boost?) then remapping will increase this pressure and lead to premature failure of the diaphagm?

Would that make sense TT?

Sam

The PCV valve has NOTHING to do with turbo boost!    It is ONLY the DV which is affected by turbo boost, unless you have modified your engine to work on the two stroke cycle!

The PCV valve may have nothing to do with boost,  but it can be affected by it.  Therefore increased boost can damage it.

Crankcase Ventilation

The crankcase is maintained in a constant
vacuum while the engine is running.
The crankcase breather that supplies
this vacuum is connected to the intake
manifold.
The crankcase blow-by gases are separated
in two stages. In the first stage, the
primary oil separator in the oil filter module
takes most of the oil out of the gases. A
second separator in the cylinder head cover
removes the remainder of the oil from the
gases.
Since a turbo engine requires a more
sophisticated pressure control system, a
two-stage pressure control valve is located
on the cylinder head cover. If vacuum exists
in the intake manifold, blow-by gases flow
directly into the intake manifold.
If a boost pressure is present in the intake
manifold, a one-way valve in the pressure
control valve housing closes and the blowby
gases flow into the cylinder head cover
ahead of the turbocharger. The system can
detect faulty installation of the pressure
control valve. Unmetered air is detected by
the reaction of the oxygen sensor.

Where - exactly did that blatant cut, copy and paste come from?  Because that categorically is NOT from a Volkswagen Group FSI engine?  And there are some serious, and fundamental basic errors with that!

And I will categorically state again, boost pressure has absolutely NOTHING to do with the PCV - nothing!  Furthermore, it can NOT be affected by boost either.

But hey, you read and stole the above from some other internet forum, so that then means it must be true!