hard jerk under throttle in low rpm in 1st, 2nd gear - Page 2
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This is a discussion on hard jerk under throttle in low rpm in 1st, 2nd gear within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; nope it only bucks once when i press the throttle when the revs are below 2000, also when i release ...

  1. #16
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    nope it only bucks once when i press the throttle when the revs are below 2000, also when i release the throttle when the revs are below 2000 it also bucks once. could this be another issue or a combonation of issues?

    it feels like driveline lash to me but im not 100% sure

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  3. #17
    Admiral Ackbar the 1st mycologist's Avatar
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    Quote Originally Posted by Sarra View Post
    My WRX is my 5th Subaru. Weirdly enough, all of my Subies have had 80K or more (miles, not KMS) on them, including my WRX. So far, my WRX has been the smoothest at low RPM's, especially in first gear. 2 mph, first gear, left foot on the dead pedal, play with the gas a little and it is smooth. My previous cars were another story, especially the 1985 GL Turbo, but that car had 290+K on it. If it's jerky, then I would suspect something is worn out or needs to be tightened, go to someone who knows suspensions well and ask their opinion.
    This is unusual. Are your bushings stock?
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  4. #18
    Moderator YBNormal07's Avatar
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    Full engage the e-brake. Pop the hood. Start the car and peer under the bottom of the hood or have someone standing there who can watch the engine.

    Give it some throttle and slowly release the clutch enough to start dropping RPMs. Watch the engine. If it moves up or over more than an inch, you've got a busted motor mount.

    Another alternative is to do a hard shift from 1st to 2nd, trying to release the clutch as fast as possible. If you hear a thump from the engine area, it's a broken motor mount.

    This is usually pretty violent, so it doesn't sound like a broken mount, but it may be cracked or loose too.

    Have you examined the pitch mount and trans bushings yet? They could also be the culprit.

    Really, it's a matter of perception too. What may feel like bucking to you may not even be noticed by someone else. If it is only doing it below 2K rpm moving up or down on the throttle, it almost sounds like an engine management issue. If it were drivetrain lash, it would appear at other rpms.

    When it bucks, can you hear the trans teeth making an rrrrrr-rrrr-rrrrr sound...kind of like a faster version of a semi truck as it initially starts from a dead stop? If so, it's just lash. If not, I'd say EM or motor mount.

    EM will have to fixed via aftermarket (Cobb, etc) or dealership reflash.
    Motor mounts are easy to fix. Trans mount is a bit harder. Never done a pitch mount.
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  5. #19
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    hmmm i will try that, i dont think i hear anything when the car bucks

    if it is an EM issue, since my car is stock, would resetting the ECU by unhooking the battery help at all? i will try this tonight

  6. #20
    Registered User wrx0131's Avatar
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    Quote Originally Posted by poopeebum View Post
    hmmm i will try that, i dont think i hear anything when the car bucks

    if it is an EM issue, since my car is stock, would resetting the ECU by unhooking the battery help at all? i will try this tonight
    If your car is completely stock then there is no need for EM.
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  7. #21
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    Quote Originally Posted by wrx0131 View Post
    If your car is completely stock then there is no need for EM.
    My mistake...I should have said ECU.
    tEh PriUs=teH faSTah!@@!
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  8. #22
    Moderator YBNormal07's Avatar
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    Quote Originally Posted by poopeebum View Post
    hmmm i will try that, i dont think i hear anything when the car bucks

    if it is an EM issue, since my car is stock, would resetting the ECU by unhooking the battery help at all? i will try this tonight
    I can't hurt, and usually give a short term performance boost until the ECU "relearns". If you aren't hearing anything, and aren't getting any CELs, it is sounding more and more like drivetrain lash.
    tEh PriUs=teH faSTah!@@!
    08 Audi S5 Black Diamond edition
    SOLD: 05 SWP Legacy GT Limited 5MT, 13.3ish@105 (stage 2) crappy stock clutch
    SOLD: 04 MPS/SW WRX Sti. 12.971 @ 103.97 (stock)
    278 AWHP/283 AWT, Catback exhaust
    306 AWHP/341 AWT, Stage 2
    (Scott) Moderator-STi, Drag Racing, Car Purchasing, and Tutorial Forums

  9. #23
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    i really hope its not any of my engine mounts, hopefully its just the pitch mount that needs replaceing.

  10. #24
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    Situation Update!:

    So I have replaced the transmission mount with a STi Group N mount, replaced the transmission crossmember bushing with kartboy's race bushings, added the kartboy rear diff outrigger bushings, and a beatrush aluminum pitch stop. I have the STi Group N engine mounts but I havent installed them yet.

    In regards to the jerking in 1st and 2nd gear under low rev throttle i do notice improvement, the jerks are less apparent but it still does happen.

    I am beginning to suspect that there could be another cause for the bucking issue since i had the car ive been using shell 91 octane gas. For my latest fill up i used 94 octane gas from Husky which is the 10% ethanol blend. My engine idling, revving and under load became noticibly smoother! the bucking and jerking in 1st & 2nd gear is barely noticible now. After I go through this tank i will go back to using 91 octane and see if the jerking comes back, i do notice my engine ran rougher with 91 octane though. could the jerking and bucking be related to the octane of gas im using? could the engine be knocking or misfiring? i haven't gotten a single check engine light.

  11. #25
    Admiral Ackbar the 1st mycologist's Avatar
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    If you can get higher than 91, use the highest you can. 91 is marginal at best for a WRX.
    "From a little spark may burst a mighty flame." - Dante
    "The stitch is lost unless the thread is knotted." - Italian proverb

  12. #26
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    Could it be the CDV? (Clutch Delay Valve)
    You normally feel that in 1st and 2nd gear.
    There is some good write ups on iwsti on how to
    take it out.

  13. #27
    Moderator YBNormal07's Avatar
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    Quote Originally Posted by 23-10 View Post
    Could it be the CDV? (Clutch Delay Valve)
    You normally feel that in 1st and 2nd gear.
    There is some good write ups on iwsti on how to
    take it out.
    Nope...that just makes it feel like your clutch is not engaging at all....plus you get a nice distictive clutch burning smell half the time. I hate those CDVs...however invented them should be "re-engineered"
    tEh PriUs=teH faSTah!@@!
    08 Audi S5 Black Diamond edition
    SOLD: 05 SWP Legacy GT Limited 5MT, 13.3ish@105 (stage 2) crappy stock clutch
    SOLD: 04 MPS/SW WRX Sti. 12.971 @ 103.97 (stock)
    278 AWHP/283 AWT, Catback exhaust
    306 AWHP/341 AWT, Stage 2
    (Scott) Moderator-STi, Drag Racing, Car Purchasing, and Tutorial Forums

  14. #28
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    Question about the CDV: Is the clutch delay valve the reason that sometimes when i think i have the revs matched perfectly and i let go of the clutch it still jerks a bit? feeling like a bad shift?

    Also to further update to my jerkyness situation: I've pretty much figured out whats causing it in my case. It was a combination of poor quality gas and the stock ecu tune. I'm currently running a opensource stage1 map and the jerkyness in 1st and 2nd are gone. It does sometimes happen when the car is cold but very rarely now.

  15. #29
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    EVEN FURTHER UPDATE!!!

    I still had a bit of jerkeyness starting from a stop from what I thought to be from the OTS stage 1 map i downloaded. I was wrong!

    So....I FINALLY installed the Turn In Concepts Rear Diff Bushings (race) tonight that I had sitting in my garage since September last year! What a HUGE difference these solid bushings make!! These things completely remove the jerkyness when accelerating from a stop. I wish I had installed these right away last year. There is increased noise, harshness, vibrations but i dont really care, its totally worth it, this car finally drives like it should.

  16. #30
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    Quote Originally Posted by poopeebum View Post
    EVEN FURTHER UPDATE!!!

    I still had a bit of jerkeyness starting from a stop from what I thought to be from the OTS stage 1 map i downloaded. I was wrong!

    So....I FINALLY installed the Turn In Concepts Rear Diff Bushings (race) tonight that I had sitting in my garage since September last year! What a HUGE difference these solid bushings make!! These things completely remove the jerkyness when accelerating from a stop. I wish I had installed these right away last year. There is increased noise, harshness, vibrations but i dont really care, its totally worth it, this car finally drives like it should.
    sorry for the epic bump, need help on this issue.

    hey poopeebum,

    I am experiencing hard jerk in low speed (1st and 2nd gear, in low RPM) as well. Seems like the exact same symptom as you described.

    So, what is the parts do you recommend in changing in sequence?

    Change the rear differential bushings to TIC first ??

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