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Catch can install, idles rough now?

S

Slothy

Distrusts the trustworthy
Location
BC, Canada
Car(s)
2008 GTI
Had a longer post typed but decided TLDR, so:

Had a 42DD catch can installed the other day and noticed two things:

1) Sounds different at idle - noise comes out of the engine intake, can be stopped by pinching either of the hoses going to/from CC, sounds like it is idling a bit rough.

2) Pulling the oil dipstick on the engine does not effect idle. I very specifically remember it used to when I first purchased the car a few months ago and had no catch can. Uncovering CC dipstick hole causes noise to lessen/stop. Covering it again causes it to start again after a second or two.

Is the above normal? I've seen the thread about the rear breather with the valve in it, but AFAIK they haven't replaced it since I first pulled the oil dipstick while at idle a few months ago.
 
Moosecakes

Moosecakes

Ready to race!
Location
eugene
Car(s)
2008 GTI
The noise you are hearing is the rear check valve through the intake. It's making a putting sound isn't it?

and as for the 2nd question I'm not sure. I'm running BSH comp catch can and I haven't bothered to pull the dip stick out and see what happens. Because the catch can/pcv solution is intended to remedy the issue that is identified by pulling the dip stick. I honestly wouldn't worry about that.

But define rough idle? do you have vag com? check for vac leaks. Those are going to be the common cause of a funky idle.
 
S

Slothy

Distrusts the trustworthy
Location
BC, Canada
Car(s)
2008 GTI
No vag com. Thought about buying one shortly after I bought the car but never quite got around to it. Will have to see if I can bribe someone in my area with beer.

I guess it does kind of sound like a boat motor at idle, if that's the kind of putting you're talking about? Not sure what else really to describe it as.
 
S

Slothy

Distrusts the trustworthy
Location
BC, Canada
Car(s)
2008 GTI
Thanks, that video wasnt making it through the firewall last time I saw the thread. Sounds some-what like mine; I'll give it another listen when I'm at home with proper speakers instead of this laptop junk.
 
Last edited:
kruegernaut

kruegernaut

I'm from Detroit, Man...
Location
Washington
OP did you find resolution on this? I also have no vac at the dipstick after installing my catch can. I did remove the rear pcv to stop the intake noise. But I thought there was supposed to be some vac at the dipstick. My fuel trims are high so Im trying to determine if I have a vac leak.
 
R

Rajini98

.
Location
NC
kruegernaut said:
OP did you find resolution on this? I also have no vac at the dipstick after installing my catch can. I did remove the rear pcv to stop the intake noise. But I thought there was supposed to be some vac at the dipstick. My fuel trims are high so Im trying to determine if I have a vac leak.
Click to expand...

The point of the PCV fix that a catch can provides is that you dont have a rough idle if the crank case is exposed to the atmosphere. Since there is no longer a path to the intake after the throttle body anymore, your idle does not change.
 
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