RB25 rough idle - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Billcriss · 05-07-2017, 07:29 AM

I have the CXracing intercooler kit with there BoV. The car runs fine but at idle it acts like it has a HUGE Cam. To the point where it damn near shuts off. But when I rev it, it's fine. Any idea?

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Juantwo3 · 05-07-2017, 08:45 AM

How is you iacv set up, are you using a greddy intake manifold or oem one

Billcriss · 05-07-2017, 08:53 AM

Quote:

Originally Posted by Juantwo3

How is you iacv set up, are you using a greddy intake manifold or oem one

Im using the OEM one.

#9 is going to my boost gauge
#8 is capped off
#7 and #6 is going to my BOV

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Billcriss · 05-07-2017, 09:11 PM

anyone got any ideas?

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feito · 05-07-2017, 09:33 PM

Im assuming your bov is recirculated

sblack13 · 05-07-2017, 10:47 PM

Shouldn't #8 Goto brake booster?

djdryon · 05-08-2017, 02:07 AM

A recirculated bov helps a lot with stabilizing the idle. Also, why do you have two hoses going to a bov?

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Billcriss · 05-08-2017, 04:48 AM

Quote:

Originally Posted by djdryon

A recirculated bov helps a lot with stabilizing the idle. Also, why do you have two hoses going to a bov?

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Honestly I have no idea. The OEM one had 2 so I assumed that's what I needed to do. The BOV does have two nipples though...

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Billcriss · 05-08-2017, 04:49 AM

Quote:

Originally Posted by sblack13

Shouldn't #8 Goto brake booster?

I don't have a brake boost. I have the boost delete from chase bays

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djdryon · 05-08-2017, 05:16 AM

Quote:

Originally Posted by Billcriss

Honestly I have no idea. The OEM one had 2 so I assumed that's what I needed to do. The BOV does have two nipples though...

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Interesting. Never seen a bov with 2 hoses. I don't see why you couldn't just use one hose with a splitter...

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Billcriss · 05-08-2017, 05:21 AM

Quote:

Originally Posted by djdryon

Interesting. Never used a dual port bov. I don't see why you couldn't just use one hose with a splitter...

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no idea if this is right but this is how I assumed it should be. Could very well be wrong

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djdryon · 05-08-2017, 05:45 AM

That's a strange design. Both hoses applying equal pressure/vacuum to each side of the piston/diaphragm would totally negate each other... I know that design is used for wastegates, but each side gets air from a different source.
By design the top port goes to the intake, so the valve is held shut under boost and pulled open under vacuum (when the throttle plate is closed) I can only imagine the bottom one would go to an opposing force, so pulling under boost and pushing under vacuum... but how this would be plumbed in...

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RB25GUY · 05-08-2017, 05:48 AM

bottom line needs to be open on the BOV. A tune might help aswell.

Billcriss · 05-08-2017, 05:53 AM

Quote:

Originally Posted by RB25GUY

bottom line needs to be open on the BOV. A tune might help aswell.

So cap one of the nipples on the intake and leave the bottom nipple on the BOV open? The goal is to get a power FC in a few weeks to and a few more goodies. But I need this to start acting like it should lol

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djdryon · 05-08-2017, 06:05 AM

Quote:

Originally Posted by Billcriss

So cap one of the nipples on the intake and leave the bottom nipple on the BOV open? The goal is to get a power FC in a few weeks to and a few more goodies. But I need this to start acting like it should lol

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Yes, try that. If the bov is staying open at idle, you'll have a vacuum leak, which will cause a rough idle.

Did some reading and if yours is a dual spring bov (and you are recirculating), I guess you can have them both from the intake, but make sure they're connected to the SAME source, so there's no pressure differentiation.

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feito · 05-08-2017, 07:50 AM

Next time dont assume and do more research. That vta freddy bov wont give you a vac leak, but it will leak air out at idle. This is a very old and well discussed topic, you should have done more research on it.
Just recirculate that bov and leave the bottom nipple Disconnected

Billcriss · 05-08-2017, 05:57 PM

Quote:

Originally Posted by feito

Next time dont assume and do more research. That vta freddy bov wont give you a vac leak, but it will leak air out at idle. This is a very old and well discussed topic, you should have done more research on it.
Just recirculate that bov and leave the bottom nipple Disconnected

Should I cap 7 or 6?

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dwnshft2drft · 05-08-2017, 06:26 PM

Download FSM and BOV manual just to double check stuff. Cleaning IACV and throttle body would help idle.

djdryon · 05-08-2017, 07:05 PM

Quote:

Originally Posted by feito

recirculate that bov and leave the bottom nipple Disconnected

What he said [emoji115]

Quote:

Originally Posted by Billcriss

cap 6 or 7?

I'd cap the lower one, since it'll give you a cleaner-looking install. Best way ive found is a nipple cap with a hose clamp. Been holding fine on my KA-T for years with 15psi. Do the same with the one you stuck a bolt in.

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Billcriss · 05-09-2017, 05:47 PM

Seems to be running great!

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05-07-2017, 07:29 AM	#1
Billcriss Leaky Injector Join Date: May 2016 Location: Sanford, North Carolina Age: 28 Posts: 91 Trader Rating: (0) Feedback Score: 0 reviews	RB25 rough idle I have the CXracing intercooler kit with there BoV. The car runs fine but at idle it acts like it has a HUGE Cam. To the point where it damn near shuts off. But when I rev it, it's fine. Any idea? Sent from my iPhone using Tapatalk

05-07-2017, 08:45 AM	#2
Juantwo3 Zilvia FREAK! Join Date: Sep 2011 Location: DTFullerton Age: 33 Posts: 1,103 Trader Rating: (20) Feedback Score: 20 reviews	How is you iacv set up, are you using a greddy intake manifold or oem one __________________ GO DUCKS!!!!!!!!!

05-07-2017, 09:33 PM	#5
feito Nissanaholic! Join Date: May 2007 Location: Texas Posts: 1,999 Trader Rating: (1) Feedback Score: 1 reviews	Im assuming your bov is recirculated __________________ Tuners are big bullies

05-08-2017, 05:45 AM	#12
djdryon Leaky Injector Join Date: Jun 2009 Location: Seattle, WA / Saitama, JP Age: 38 Posts: 112 Trader Rating: (1) Feedback Score: 1 reviews	That's a strange design. Both hoses applying equal pressure/vacuum to each side of the piston/diaphragm would totally negate each other... I know that design is used for wastegates, but each side gets air from a different source. By design the top port goes to the intake, so the valve is held shut under boost and pulled open under vacuum (when the throttle plate is closed) I can only imagine the bottom one would go to an opposing force, so pulling under boost and pushing under vacuum... but how this would be plumbed in... Sent from my SM-G935T using Tapatalk __________________ Contributions: ULTIMATE climate HVAC LED conversion.

05-08-2017, 07:50 AM	#16
feito Nissanaholic! Join Date: May 2007 Location: Texas Posts: 1,999 Trader Rating: (1) Feedback Score: 1 reviews	Next time dont assume and do more research. That vta freddy bov wont give you a vac leak, but it will leak air out at idle. This is a very old and well discussed topic, you should have done more research on it. Just recirculate that bov and leave the bottom nipple Disconnected __________________ Tuners are big bullies

05-07-2017, 09:11 PM	#4
Billcriss Leaky Injector Join Date: May 2016 Location: Sanford, North Carolina Age: 28 Posts: 91 Trader Rating: (0) Feedback Score: 0 reviews	anyone got any ideas? Sent from my iPhone using Tapatalk

05-07-2017, 10:47 PM	#6
sblack13 Zilvia FREAK! Join Date: May 2005 Location: Seattle Age: 37 Posts: 1,016 Trader Rating: (10) Feedback Score: 10 reviews	Shouldn't #8 Goto brake booster?

05-08-2017, 02:07 AM	#7
djdryon Leaky Injector Join Date: Jun 2009 Location: Seattle, WA / Saitama, JP Age: 38 Posts: 112 Trader Rating: (1) Feedback Score: 1 reviews	A recirculated bov helps a lot with stabilizing the idle. Also, why do you have two hoses going to a bov? Sent from my SM-G935T using Tapatalk __________________ Contributions: ULTIMATE climate HVAC LED conversion.

05-08-2017, 06:26 PM	#18
dwnshft2drft Zilvia Addict Join Date: Dec 2006 Location: 3 stars n a sun Posts: 675 Trader Rating: (28) Feedback Score: 28 reviews	Download FSM and BOV manual just to double check stuff. Cleaning IACV and throttle body would help idle.

05-09-2017, 05:47 PM	#20
Billcriss Leaky Injector Join Date: May 2016 Location: Sanford, North Carolina Age: 28 Posts: 91 Trader Rating: (0) Feedback Score: 0 reviews	Seems to be running great! Sent from my iPhone using Tapatalk