engine revs when lifting off gas
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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; Some times when i shift, at say 3000 rpm, when i let off the gas, the engine will run up ...

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    Registered User wrxwex's Avatar
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    engine revs when lifting off gas

    Some times when i shift, at say 3000 rpm, when i let off the gas, the engine will run up like 500 rpms very quickly then fall, am i letting off the gas too slowly, or is this a common problem, btw, my car has about 300 miles on it now. thanks
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    Re: engine revs when lifting off gas

    Originally posted by wrxwex
    Some times when i shift, at say 3000 rpm, when i let off the gas, the engine will run up like 500 rpms very quickly then fall, am i letting off the gas too slowly, or is this a common problem, btw, my car has about 300 miles on it now. thanks
    IIRC, I think it is an emmisions related issue, where the ecu has the engine to burn up excess gas or something to that nature...
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    Registered User PolarisSnT's Avatar
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    Its the fact that our flywheel is so heavy that the inertia causes it to spin up alittle when you let off the gas and on the clutch during a shift. Atleast this is the general consensus around here.
    Dan- 2004 PSM 5spd

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    Registered User wrxwex's Avatar
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    i don't think its related to the flywheel because after i let off, the engine actually increases speed faster than it was while i was accelerating, its more of a hiccup when i let off, and it doesn't happen on every shift, ill try to pinpoint it on the drive home from work today, thanks for the responses!
    2004 PSM sedan - 5 speed
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    Banned hippy78's Avatar
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    maybe it has something to do with the cruise control recall?

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    I thought someone said in some thread it is the BPV. Because it redirects air back into the intake. I have the same thing with my car running the stock bypass valve, just let off the gas a little before you clutch in.
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    Registered User Fixxxer's Avatar
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    Originally posted by hippy78
    maybe it has something to do with the cruise control recall?
    Nope. I went and got mine fixed. All they did was snap a little clip on there to be sure the cable doesn't come out of its track.

    And, FWIW, my car has this problem too. I think it's because of the BPV as well.
    -Lee

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    Registered User psychobooe's Avatar
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    I have experienced this same problem as well. I thought that maybe I was just holding the gas down too long or something. I'm glad to hear that it's not my driving.

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    Banned hippy78's Avatar
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    Originally posted by psychobooe
    I have experienced this same problem as well. I thought that maybe I was just holding the gas down too long or something. I'm glad to hear that it's not my driving.
    Who said it isn't? All these people could be doing the same thing with their feet. I mean, does it happen all the time? Have you tried letting the gas out a little earlier when pressing on the clutch?

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    Registered User psychobooe's Avatar
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    The only way that I can get it to not happen is if I let off the gas like 2 seconds before I engage the clutch. I'm pretty sure it's not supposed to happen like that.

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    let off the gas, count "one-onethousand", then clutch in. Then come back and tell us the engine continues to accellerate. Odds are you guys are just mis-timing your shift.

    If you're waiting a beat before clutching and it STILL revs up, you may have a legit problem. Until then I vote operator error.
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    Well one thing I have noticed, and it is why I know it is the BPV, is when I am on boost and I clutch in the rpms will jump up. If I am not on boost they will not. If you have a boost gauge all you have to do is wait untill the boost falls off before you clutch in, or just deal with it and wait a little longer to get into the next gear. Another thing that would resolve this issue would be a BOV, but then you are risking all kinds of problems and it is an extra $200+ to get one.
    Evan
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    Registered User blarg's Avatar
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    I think someone on I-club attributed this problem to "boost surge" or something. Basically when you take your foot off the gas, the intake is still pressurized, so is the fuel line, and the turbo is still spooled, and it takes a split second for the ECU to correct for this. Usually caused when you start pushing the clutch WHILE you're coming off the gas...NOT fun when you're shifting near redline. I think you learn to avoid it after driving for a while. I noticed I don't have this problem with a 100% ATM BOV, maybe because the system depressurizes faster (then you stilll have the same amount of gas going in, but less air to burn it --> lean condition associated with BOV'S).

    or maybe I'm just on crack.
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    Registered User PolarisSnT's Avatar
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    Originally posted by blarg
    (then you stilll have the same amount of gas going in, but less air to burn it --> lean condition associated with BOV'S).

    or maybe I'm just on crack.
    Same fuel with less air= rich not lean.

    It happens to me on every shift and doesnt when I drive other cars, so i dont know.
    Dan- 2004 PSM 5spd

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    Registered User wrxwex's Avatar
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    its not a problem right? - theres nothing wrong i don't think, even if there was, its so minor its not a problem
    2004 PSM sedan - 5 speed
    helix rsb + endlinks/gutted uppipe/whiteline steering rack bushings
    stg II next spring...
    AIM: maxler3
    gutted up pipe for sale - $60 shipped anywhere in the US. pm for details

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