Help! Turbo varies speed while throttle is held wide open
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This is a discussion on Help! Turbo varies speed while throttle is held wide open within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; I just bought a 2004 WRX with 80k miles on it. It seems like a good car except when I ...

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    Help! Turbo varies speed while throttle is held wide open

    I just bought a 2004 WRX with 80k miles on it. It seems like a good car except when I give it full throttle, I can hear the turbo go full speed but then slow down then go full speed then slow down etc. I don't alter the throttle at all when this occurs. You can feel the acceleration changing, too.

    Not sure what other info could be useful. The car was in Phoenix it's whole life and now it's in Montana. I think it will do it in all gears but it's hard to notice in 1st, 2nd, & 3rd, easy to notice in 4th and easier to notice in 5th.

    I'm wondering if it's not getting enough fuel so the turbo automatically slows down. I really have no idea and all my searches for info come up with zero results. Any help would be much appreciated.

    Also, my car is completely stock.
    Last edited by snake2332; 01-27-2008 at 09:20 AM.

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    Registered User teflon_jones's Avatar
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    Sounds like your BPV may not be working correctly.
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    So the bypass valve is not the same as the blow-off valve? They kinda look the same http://www.turboxs.com/shop_prod.php?what_category=2

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    Registered User apex32's Avatar
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    Quote Originally Posted by snake2332 View Post
    So the bypass valve is not the same as the blow-off valve? They kinda look the same http://www.turboxs.com/shop_prod.php?what_category=2
    BOV and BPV are very different. Only use a BPV on your wrx, they dont play nice with BOV's

    BOV is what dumps to atmosphere and makes the pshhh noise. BPV recirculates and doesnt screw with your MAF
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    Quote Originally Posted by RealDealTarheel View Post
    They're usually way too busy popping their BOV's at me anyways. If I put an anti-neon sign on my FMIC I'd really never get to grocery shop in peace.

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    Mods....? sounds like an over boosting problem.

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    Registered User apex32's Avatar
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    Quote Originally Posted by Not-EWRX View Post
    Mods....? sounds like an over boosting problem.
    OP says completely stock
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    Quote Originally Posted by RealDealTarheel View Post
    They're usually way too busy popping their BOV's at me anyways. If I put an anti-neon sign on my FMIC I'd really never get to grocery shop in peace.

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    OK thanks for the help. I'm a newbie still and yes it's completely stock still.

    Do you think I'd benefit from getting a Turbo XS bypass valve over just a replacement OEM one from Subaru?

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    OK I said "darn it" and bought a Turbo XS RBV (reverse bypass valve) for $175 shipped. Hope it fixes the problem. If not, at least I have a better-than-stock BPV.

    Thanks for the info! I'll update this with whether or not it fixed my problem in a couple weeks.
    Last edited by 06wrx4me; 01-29-2008 at 11:49 AM. Reason: Please dont dodge the swear filter

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    Registered User sigurd's Avatar
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    Quote Originally Posted by Not-EWRX View Post
    Mods....? sounds like an over boosting problem.
    Yup your over boosting and the car is trying to correct itself. doesnt matter that it is stock.

    if you had a boost gauge you would see it doing it. Probably going from 15/16psi down to 8psi and back and fourth.

    Things to check:

    Make sure your restrictor pill is in place. Make sure all your vacuum hose from the boost control solenoid to the compressor housing to the wastegate is in place not cracked and orentated correctly.

    here is a good diagram so you can check it with your car.


    Also if the wastegate arm has been shortened by the previous owner too far this can cause the same issue. Some people do this to reduce wastegate flutter but if done to far can cause issues.

    pretty much your car is getting to much boost and the boost control system freaks out and over compensates to reduce boost causing it to surge like that.
    Last edited by sigurd; 01-29-2008 at 11:42 AM.

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    BPV didn't change the problem

    I've been so busy moving in with my girlfriend lately that I haven't gotten a chance to update this thread. The bypass valve didn't change the problem. It didn't change the behavior at all. I'll check the things that Sigurd suggests when I install the cold air intake sometime in the next week or two.

    Thanks for the info & diagram Sigurd!

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    Moderator Donkey's Avatar
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    I would save you money with the cold air intake and buy a Tactrix cable instead if you have a lap top.It makes a great diagnostic tool even if you have know idea what your looking at.You can log the car and post the datalog allowing more experienced people to look and see almost exactly what is going on by the parameters logged.Do you have a boost gauge?Might want a good set of gauges before you go and start buying all kinds of performance parts.The more you parts you add,the better chance of problems happening.So either your overboosting,which you should be hitting the fuel cut and possibly getting a CEL.Or you are just getting boost oscillations and the wastegate arm needs to be adjusted.But in order to tell the difference between the two you would need a boost gauge.If the car is completly stock including exhaust I don't think it's overboosting due to so much back presssure and catted up-pipe.
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    Quote Originally Posted by Donkey View Post
    I would save you money with the cold air intake and buy a Tactrix cable instead if you have a lap top.It makes a great diagnostic tool even if you have know idea what your looking at.You can log the car and post the datalog allowing more experienced people to look and see almost exactly what is going on by the parameters logged.Do you have a boost gauge?Might want a good set of gauges before you go and start buying all kinds of performance parts.The more you parts you add,the better chance of problems happening.So either your overboosting,which you should be hitting the fuel cut and possibly getting a CEL.Or you are just getting boost oscillations and the wastegate arm needs to be adjusted.But in order to tell the difference between the two you would need a boost gauge.If the car is completly stock including exhaust I don't think it's overboosting due to so much back presssure and catted up-pipe.
    Well I already bought some parts for it, like:

    cold air intake
    perrin intercooler hoses
    turboxs bypass valve
    underdrive lightweight pulley kit
    ngk iridium spark plugs
    catless invidia uppipe
    infinity speakers and momo shift knob

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    So do you think I should try lengthening the wastegate arm and test driving it to see if that is the problem? I don't have a boost gauge yet, maybe I should wait to diagnose the problem further until I have one. Do you think I could cause any harm by lengthening the wastegate arm? Or by shortening it? Do you know what else could cause the boost hitting the boost limit like it's probably doing? I noticed a thread hanging off of a plug down under the drivers side dash by the hood-release lever, like by my left knee. Wondering why the previous owner tied a thread to it. Where is the plug at that you would hook an AccessPort to?

    Sorry I have so many questions, I'm still a newbie.

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    Registered User Findus11's Avatar
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    OK guys lets keep this thread alive
    please
    I have the same problem with my 07
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    Quote Originally Posted by Findus11 View Post
    OK guys lets keep this thread alive
    please
    I have the same problem with my 07
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