# someone explain reason behind the 'ISV'



## Bejbis (Mar 28, 2001)

guys, i wanna know, why do we have those goofy freakin idle stablizer valves? it dosnt really perform a function other than get in the way and clutter up the engine bay....i mean yea, it stablizes the idle....big freakin deal....you can 'stabilize' the idle by that little screw on the throttle body. thats how all other cars work. set the screw and your car idles at 1000, 1200, 1400....depending on how you set it. someone please explain to me why we have these stupid things....
Daniel







<---me and my buddy spongebob are confused.....


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## gearhead455 (Oct 30, 2001)

*Re: someone explain reason behind the 'ISV' (Bejbis)*

The ISV was added to stabilize the idle to a specific RPM when various devices turned on and off that would affect the idle. Canister purge valves, A/C compressors, power brake vacuum drop all can effect idle slightly. The slight variations where compensated with the ISV. Most fuel-injected engines use some sort of idle stabilizer.
The ISV can also be commanded to "idle up" when the engine is cold.
I use no ISV, just an idle air bypass valve... it works fine. Idle does vary a little but not enough to be a problem.



[Modified by gearhead455, 2:47 AM 9-6-2002]


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## Bejbis (Mar 28, 2001)

*Re: someone explain reason behind the 'ISV' (gearhead455)*

thanks for the info buddy......i disconnected mine tonight and plugged up hole in the manifold.....gave me 2 more psi from my g60.....yay.....my 944 dosnt have an idle stablizer....








Daniel


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## euroscene (Feb 28, 2001)

*Re: someone explain reason behind the 'ISV' (Bejbis)*

its one of those vw things that are added to make working on them harder.


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## scirocco16v (May 17, 2000)

*Re: someone explain reason behind the 'ISV' (euroscene17)*

The ISV was to my understanding, primarily the replacement for the AAR (Auxilary Air Valve)...which was there to allow more air flow at cold startup to keep the idle higher...It seems as though it's also a 2 in 1 as it would also function as an idle boost valve (for AC etc.) hmm... I'd think it's a good thing.


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## 2035cc16v (May 18, 2000)

*Re: someone explain reason behind the 'ISV' (scirocco16v)*

it is a good thing until it goes bad and you try and justify spending 170 bucks on a new one... btw I have an alomst new 8v one ( maybe 100 miles then a year in the parts drawer) from back in the day if someone needs one...


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## 8vgtiofdoom (Mar 8, 2004)

*Re: someone explain reason behind the 'ISV' (2035cc16v)*

hey what 8v did it come off of? numbers 037 906 457C or 037 906 457D?


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## L33t A2 (Aug 5, 2003)

*Re: someone explain reason behind the 'ISV' (8vgtiofdoom)*

some guy has about 10 of them for sale all around 30 bux
search for isv bank


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## 85GTI CA (Apr 7, 2004)

*Re: someone explain reason behind the 'ISV' (L33t A2 Jetta)*

just take off the isv! Mine actually ran better without it (better response). I just needed to adjust the idle.


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## grayfox (May 13, 2003)

*Re: someone explain reason behind the 'ISV' (85GTI CA)*


_Quote, originally posted by *85GTI CA* »_just take off the isv! Mine actually ran better without it (better response). I just needed to adjust the idle.









same here, i have no idle stabilizer and made a big differnce, idles and starts up better


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## SA16v (Jul 14, 2004)

*Re: someone explain reason behind the 'ISV' (grayfox)*

What i am interested in knowing - is when you car has been standing all night and you get to your car to start it, does it start up fine (smooth) or does it start up and idles rough and you have to keep your foot on the pedal to let it idle... for those of you who have removed the ISV.


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## xzenom (Nov 30, 2003)

*Re: someone explain reason behind the 'ISV' (SA16v)*

I think there are 2 symptoms from a bad ISV:
* If your car starts just fine when cold and the revs increase for a while after startup, but when the revs return to normal the idle becomes rough etc. That could mean that your ISV or AAV isn't shutting proberly so that a small ammount of air can still pass it.
* If your revs doesn't increase at all when starting cold


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## wclark (Mar 28, 2001)

*Re: someone explain reason behind the 'ISV' (SA16v)*


_Quote, originally posted by *SA16v* »_What i am interested in knowing - is when you car has been standing all night and you get to your car to start it, does it start up fine (smooth) or does it start up and idles rough and you have to keep your foot on the pedal to let it idle... for those of you who have removed the ISV.

With the ISV removed and the bypass ports on the manifold plugged mine requires I maintain some throttle on startup for a few seconds to keep the idle over 1000 or it will stall. When warmed up the idle is lumpy because of the cam and the RPM it idles at depends on how warm it is. The range is 1000 (cold) -1400 (hot) RPM and was set with the throttle closed position adjustment screw.


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## Zekes89Jetta (Jun 14, 2003)

*Re: someone explain reason behind the 'ISV' (wclark)*

Whats involved in removing the ISV? The buggered "keeper clip" on my 89 Carat w/Digi2 would let the harness connector plug come off off the ISV and the engine would die. How do you do the bypass?


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## wclark (Mar 28, 2001)

*Re: someone explain reason behind the 'ISV' (Zekes89Jetta)*

Remove the assembly and plug the 2 holes in the intake.
Set the throttle idle position stop screw, or the throttle bypass screw for an acceptable idle speed when the engine is warm. I used the throttle idle screw (this will probably move the throttle off the idle sense switch.
Note, that upon startup you will probably need to attend to the throtle manually to keep the car running for a minute until the engine controls begin to see output from the O2 sensor and can then manage the engine. When cold the engine will idle at a lower RPM than when warm and this may dictate just how low a fixed idle position you can set with the stop screw.


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## vdublegend (Feb 9, 2004)

i got a 16v, but same application, have standalone with crazy cams.
Fan and p/s causes idle drop off, trying to find a working isv to solve.


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## AnthonyLawson (Sep 9, 2011)

Can anybody answer this for me? Trying to do an MK4 intake swap on a MK3 obd1, was told I'd have to find a way to make the ISV work because the only DIY was for an OBDII.... after reading this thread I'm thinking I can just take the thing off and plug it up... 


Correct me if I'm wrong.


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## WaterWheels (Aug 14, 2005)

Can't say for sure as these are US models but does the Mk4 not have a motor in the throttle body which controls the idle? If so then your older ECU will not drive the idle control motor. So the older throttle body will have to be used if it bolts directly on and some way to connect the ISV. Without it you will have nagging cold start, cold weather, engine load idle problems. OK for a race engine but for a daily driver it gets old fast.


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