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This is a discussion on engine revs when lifting off gas within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; Oh hey 10 year old thread!...

  1. #46
    Pro Manscaper Mikie13's Avatar
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    Oh hey 10 year old thread!
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  3. #47
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    oh, if anyone is still having issues.. someone had mentioned that the cruise control cable could be the culprit.. i took mine off, still has issues.. i'll put a little more slack in my throttle cable to see if it makes a difference. but i have my doubts. just curious, my code reader active readout shows my throttle at 10.6% always with the butterfly completely shut.. anyone else know what theirs shows? wonder if i have a bad tps. it does increase of course when i rotate it..

  4. #48
    Registered User Crazyced's Avatar
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    Quote Originally Posted by Mikie13 View Post
    Oh hey 10 year old thread!
    Yet I was wondering about the exact same thing. Quite annoying. Sounds like I can't time my clutching.
    2004 Subaru Impreza WRX
    2004 Dodge Neon SRT-4

  5. #49
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    like others have said.. doesn't do it at higher rpms.. only around 3-4k range.. and only when building boost. thinking possible bpv issue.. i get flutter as well when at interstate speed in 5th gear and i boost. so i may try to find another bpv to try.

  6. #50
    OMG WTF MainFrame's Avatar
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    Quote Originally Posted by callofgeorge View Post
    oh, if anyone is still having issues.. someone had mentioned that the cruise control cable could be the culprit.. i took mine off, still has issues.. i'll put a little more slack in my throttle cable to see if it makes a difference. but i have my doubts. just curious, my code reader active readout shows my throttle at 10.6% always with the butterfly completely shut.. anyone else know what theirs shows? wonder if i have a bad tps. it does increase of course when i rotate it..

    What issue? This is normal operation for these cars, so I wouldn't call it an issue. And your throttle stays slightly open because your car is DBW.. there is no IACV anymore on the DBW cars, they use the throttle plate itself to regulate idle. If it closed all the way your engine would die every time you took your foot off the gas.


    If it bothers you so much, switch over to speed density and install an atmospheric BOV.

  7. #51
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    First, my car is not DBW, its DBC.. and how does the access port increase and decrease idle then if there is no IACV? it definitely doesn't pull my throttle cable.. funny, this looks kinda like an IACV that fits my car..

    Standard AC524 Idle Air Control Valve | eBay

    I have had the throttle body off.. the butterfly is damn near closed less about .001"... and do tell why if it is not an issue, did my previous subaru not do it ever (newer stock car), and the current one doing it didn't do it until recently. i didn't change my footwork overnight.

    plus I had a friend drive it that also has a wrx.. did it to him and first thing out of his mouth was, "throttle is sticking.." so, no... i will not take "that is normal for this car" as a valid answer. you've obviously either never had the issue, or given up trying to solve it.

    please don't comment if you have no idea what you're talking about. troll elsewhere.

  8. #52
    OMG WTF MainFrame's Avatar
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    Quote Originally Posted by callofgeorge View Post
    First, my car is not DBW, its DBC.. and how does the access port increase and decrease idle then if there is no IACV? it definitely doesn't pull my throttle cable.. funny, this looks kinda like an IACV that fits my car..

    Standard AC524 Idle Air Control Valve | eBay

    I have had the throttle body off.. the butterfly is damn near closed less about .001"... and do tell why if it is not an issue, did my previous subaru not do it ever (newer stock car), and the current one doing it didn't do it until recently. i didn't change my footwork overnight.

    plus I had a friend drive it that also has a wrx.. did it to him and first thing out of his mouth was, "throttle is sticking.." so, no... i will not take "that is normal for this car" as a valid answer. you've obviously either never had the issue, or given up trying to solve it.

    please don't comment if you have no idea what you're talking about. troll elsewhere.

    Well then what kind of car do you have? All MY06+ Imprezas (and MY04+ STi) are DBW, not DBC. An AP can increase or decrease idle by changing the target parameters in the ECU, period (AP cannot actuate an IACV on its own). On a DBW car, if you use an AP to change the idle to say, 1500rpm, then the ECU reads rpm from the crank position sensor, if actual idle is lower than target the ECU sends signal to the motor in the throttle body and opens the throttle plate accordingly.

    The eBay link you posted is for a generic IACV, which clearly states it is not compatible with 2006+ model year Subarus. I never said IACVs don't exist.. you stated that your throttle plate reads open, which is how all MY06+ Imprezas control idle with the DBW throttle body. So without ever mentioning what kind of car you're talking about, I just assumed you were talking about a 2006+ Subaru. My bad for assuming.


    I've experienced rising rpm on both of my turbo Subarus, ever since I bought my first WRX new 12 years ago, drove it off the lot, that's what it did. Talked to Subaru, they said it's normal operation (due to the BPV), talked to hundreds of other owners over the years, all of their cars did the same thing.. I bought another WRX in 2008, it had a HKS SSQV installed from the previous owner. It did not have the rising rpm "issue".. that is, until I replaced the BOV with a Forge Recirculating Race BPV, then it immediately started doing the same thing. I would consider that to be normal operation.

    There's no "giving up" trying to solve something, when you already know why it happens, and how to stop it if you wanted..


    What's going on, when you release the gas under boost, the throttle plate closes, the BPV opens, air is recirculated (under pressure) back into the intake, some pushes through back into the engine, and rpms rise momentarily. When I switched back to atmospheric BOV on a SD tune it immediately stopped happening. Which makes complete sense, since the air is no longer being injected back into the engine. Talk to people running atmospheric valves, the "issue" is no longer there on their cars.






    Now, it's entirely possible that what you're experiencing is something else entirely (with similar symptoms). If what's going on with your car JUST started happening, then I would say you may have an issue, and not just the normal operation of the stock BPV. If that's the case, I would suggest creating a thread.. and if you want to get help you will need to tell people what kind of car it is that you drive, what mods it has, when the problem started, etc.

    When you had your throttle body off, was it dirty? Did you clean it? There is a normal build up of gunk from the PCV system that tends to collect in the throttle body after the butterfly valve that should be cleaned probably about every 60k miles. I suppose if that built up enough it could cause the throttle plate to stick some.
    Last edited by MainFrame; 04-11-2014 at 12:03 PM.

  9. #53
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    ASSUME = making as ASS out of U and ME.. lol.. my bad as well.. forgot this isn't nasioc.. nasioc shows what year my car is under my username.. so here are the details -

    i used to have a bone stock 2007 STI - never had issues.. it would hold rev for a second or 2 at blow off (re-circulation), but never caused revs to climb when shifting.

    current car is 05 WRX w/vf39 swap with sti pinks and ebay tmic, (sti ic cracked and leaked). cobb stage 3 AP tuned. had to have heads rebuilt due to timing belt break, did a polish on the intake, tgv's, and tb while i had them off.. cleaned everything thoroughly. re-installed everything.. ran perfect, no issues, no rev climb.. pretty sure i haven't change anything to the car and it just started doing this lovely rev climb.. and its not always.. it would be kinda intermittent..

    but for a drive by cable car, the ecu still has to open something electronically to allow air into the combustion chamber to adjust idle since it can't move the butterfly on the TB like a dbw car.

    its honestly not big enough of a deal to bother with changing to atmosphere BOV since i would have to retune.. and i will probably not put out the money on another bpv to "test" it since i only bought the car to fix and resell. its just an annoyance, and i wanted to voice my personal experience that throttle jump of anywhere from 200-500'ish rpms was not a normal thing. mine has jumped as high as around 800'ish rpm at full 18psi boost. should never do this..

    but if it is true, that its the bypassed air from the BPV is what makes the idle jump.. then why does it not jump when you shift above 5k rpms? still have boost, normally more boost, but no idle climb on shift.. only seems to do it around the 3k-4k range..

  10. #54
    Registered User wreckingball man's Avatar
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    If it is the BOV recirculating the air, then it might have something to do with the mass flow rate through the intake. 3-4k is peak boost on a stock turbo right? And at a higher rpm you have a lower pressure and compress less air with the turbo, which means less pressure (air mass) recirculating. In the lower rpm ranges, the turbo is simply not spooled up, thereby not creating any pressure to be released by the BPV, so this thing dosn't occur.

    TL DR, less boost and less mass recirculated at higher rpm, no boost and no mass flow at lower rpm, peak boost and greatest mass flow in the 3-4k rpm range which means more mass and pressure is recirculated back into the intake...just enough to cause the engine to surge a few hundred rpms.

    Just a guess. I'm sure Zax will be along later to shoot me down.

  11. #55
    OMG WTF MainFrame's Avatar
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    On DBC cars the ECU uses the IACV to let air bypass the butterfly valve for idle. It is not normal to read 10% throttle opening angle at idle with your foot off the gas, it should be 0%.. so it sounds like you definitely have something odd going on.

    From what I remember, it never mattered what rpm I was at, any release of the throttle under any amount of boost pressure would cause the rpm to jump 200-300rpm.


    Could you post some logs? I'm interested to see how the car's running on that OTS map with additional mods (I'm guessing you meant you port and polished the IM, and performed TGV deletes, etc). I would think that will probably cause problems on the stage 3 OTS map. In my experience that map runs like crap, even on cars that have the correct mods for it.

  12. #56
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    i have only made one log.. ill have to log some more and see.. i haven't even reviewed the log i have. to be honest, my a/f ratio have been kinda shaky.. up and down, but no pings yet.. no cel's.. if the previous owner was telling the truth, ( i didn't really see any markings to prove when i pulled the heads, and i didn't mic them) but the engine has a 2.2L stroker kit and crower stage 1 cams as well.. and no, not a port/polish.. i just polished with fine grit sand paper and dremel. just the outer openings i could reach. when i bought it, it also had 565 CS deatschwerks injectors with a tune from cobb in plano, tx i think.. have the dyno sheet and receipts for that.. but the new pink and AP tune run way better than the old one did.. it was super rich before. now im seeing a 14.7:1'ish at idle/consistent speed.. and around 12:1-11:1 while boosting. i was getting missfire codes on the original setup as well due to it not having a good tune..

  13. #57
    OMG WTF MainFrame's Avatar
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    Dude.. that OTS map is NOT designed for a 2.2L, or aftermarket cams. I find it really hard to believe the car runs well at all like that. Sounds like a ticking time bomb to me. With those mods, on that tune, it's only a matter of time before the engine lets go. Probably sooner rather than later.

  14. #58
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    that's why i don't think the car has these mods.. it would run way worse.. it runs too smooth with the tune to have stroker and cams.. in my opinion at least.. the stage 1 cams are only slightly longer duration same lift.. so i don't think they would affect it much. however the 2.2 would.. but the pistons did look stock, and he said they were forged flat tops.. they are flat tops, with the slightly dished square mid for valve reliefs..

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