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  1. #1
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    Default P0121 & poor performance after dyno tune

    Well i got a dyno tune today. The car ran great on the drive home for the first hour. While driving at 70mph, i tried to pass someone, the trans geared down fine, accelerated fine, then it wouldn't up shift. It stayed in the lower gear until i let off the gas completely. Then as soon as i touch the gas pedal ever so slightly the car gears down instantly and wont up shift again until i let completely off. I exited at the nearest ramp and stopped. accelerating from stop, the car just wouldn't shift right. It actually cut off when turning in to autozone. The code was p0121. Throttle Position Sensor/Switch A Circuit Range/Performance Problem. I purchased a Tps sensor, installed it there then cleared the code. I got back on 95 heading home. Everything seemed fine, i passed 3 or 4 people just like above with no issues. Then the next time i tried to pass the same thing happened. This time no code or check engine light...yet. I called the guy who tuned it, he went back to the shop and did some research on the code and feels what he did couldn't have caused it. Any Ideas anybody?

    My mods are ZZP 3" Downpipe, PLOG, 3.4 pulley, 1.9 Rockers, Wizaired CAI, Magnaflows, 180Tstat, 104's. Thanks in advance for the help.
    Last edited by nugzo; 05-09-2009 at 06:28 PM.

  2. #2
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    Default Re: P0121 & poor performance after dyno tune

    I installed factory PCM and the issue has not come back. Any ideas on what in a tune could cause TPS issues?

  3. #3
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    Default Re: P0121 & poor performance after dyno tune

    The dyno guy screwed it up.
    Sold WBody's: '03 Blue GTP/'98 Green GTP/'98 Silver GT/'05 GXP
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  4. #4
    GTP Level Member DanGTP's Avatar
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    Default Re: P0121 & poor performance after dyno tune

    Crap happens sometimes when we flash the PCM. I've had an issue before where I would load a tune and the car wouldn't run for more than a second after starting. I'd re-edit my tune and re-load it and all would be well. It's possible a byte or two got dropped in the tuning process.

    Have it re-tuned and try again.
    ~
    '97 GTP: 9.5:1 Diamonds, P&P Everything, XP, SSIC, GenV, Shiny Headers, 3.29's, HPTuners, E85

  5. #5
    Donating Users Quicklynx's Avatar
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    Default Re: P0121 & poor performance after dyno tune

    i only do "Write Calibration Only"

    IIRC you are not supposed to Flash our PCMs...
    2005 IBM Pontiac GTO, Built 4.8L .84 Twin Turbos
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  6. #6
    GTP Level Member DanGTP's Avatar
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    Default Re: P0121 & poor performance after dyno tune

    Well, that's what I meant. It's easier to say "flash" than "write calibration" or something else. I like simple words...
    ~
    '97 GTP: 9.5:1 Diamonds, P&P Everything, XP, SSIC, GenV, Shiny Headers, 3.29's, HPTuners, E85

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    Donating Users Quicklynx's Avatar
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    Default Re: P0121 & poor performance after dyno tune

    i know what you mean... but the extra 2 seconds it takes to write "write calibration only" is worth it to save someones PCM, haha
    2005 IBM Pontiac GTO, Built 4.8L .84 Twin Turbos
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  8. #8
    GTP Level Member DanGTP's Avatar
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    Default Re: P0121 & poor performance after dyno tune

    True true!
    ~
    '97 GTP: 9.5:1 Diamonds, P&P Everything, XP, SSIC, GenV, Shiny Headers, 3.29's, HPTuners, E85

  9. #9
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    Default Re: P0121 & poor performance after dyno tune

    Well it wasnt the tune. It did it again yesterday with the factory PCM. I didnt get the code this time, but got the exact same symptoms. After driving aggressive a few minutes at 80+ MPH, it just goes crazy. If i push on the pedal the slightest after it starts happening, then the car gears down and wont upshift untill i let off the gas. no matter how much or how little throttle i give it, it just winds and winds out untill 5500ish rpm. It now will do the same thing in low gears and starting from stopped, untill i turn the car off for a few minutes then all is well.

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    GTP Level Member 2000GTP's Avatar
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    Default Re: P0121 & poor performance after dyno tune

    Quote Originally Posted by nugzo View Post
    Well it wasnt the tune. It did it again yesterday with the factory PCM. I didnt get the code this time, but got the exact same symptoms. After driving aggressive a few minutes at 80+ MPH, it just goes crazy. If i push on the pedal the slightest after it starts happening, then the car gears down and wont upshift untill i let off the gas. no matter how much or how little throttle i give it, it just winds and winds out untill 5500ish rpm. It now will do the same thing in low gears and starting from stopped, untill i turn the car off for a few minutes then all is well.
    maybe something with your tps sensor? possibly
    2000 GP GTP Black 2 Door AEM Meth Injection (100% Meth), 3.25" pulley, N* TB, PRJ Wires, Smoothflow Idlers, 42# injectors, Racetronix fuel pump, ZZP Headers, 1.8 Roller Rockers, Custom CAI, NGK TR6 Plugs, 180* Tstat, Custom Tuning by TUNE TIME PERFORMANCE

  11. #11
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    Default Re: P0121 & poor performance after dyno tune

    I've thrown that code before when I unhooked the TPS sensor fooling with the MAF sensor...

    try cleaning your TPS sensor... on my car its connected to the purple relay I believe... not positive and I'm not sure if they're color coded on all cars....

    Also even though I plugged it back in I occasionally threw the code when my MAF was bad... but you are not throwing p0120 as that one has become all but too common for every one here.... MAF Failure
    2005 IBM Pontiac GTO, Built 4.8L .84 Twin Turbos
    1998 Pontiac Grand Prix Daytona Edition, Sold

  12. #12
    Donating Users Quicklynx's Avatar
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    Default Re: P0121 & poor performance after dyno tune

    another thing... remember all the sensors are quite delicate... the MAF sensor is thin metal wires, when i pulled it it did have some debris on it... i shot some compressed air on it to clean it but i still had problems.... so i got a new one and all problems disappeared
    2005 IBM Pontiac GTO, Built 4.8L .84 Twin Turbos
    1998 Pontiac Grand Prix Daytona Edition, Sold

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    Default Re: P0121 & poor performance after dyno tune

    I replaced the tps already. Thanks for the suggestions. Keep em coming.

  14. #14
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    Default Re: P0121 & poor performance after dyno tune

    Check the plug and the wires for the TPS. There's a possibility you may have a wiring issue. Who knows... Maybe it's something entirely un-related to the TPS.
    ~
    '97 GTP: 9.5:1 Diamonds, P&P Everything, XP, SSIC, GenV, Shiny Headers, 3.29's, HPTuners, E85

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    Default Re: P0121 & poor performance after dyno tune

    yea when i had the maf go bad it threw more codes than just p0120....

    have you tried unhooking the maf? unhook the MAF and drive around, see if that works... if it drives fine.. replace your MAF, and remember if you need to replace your MAF make sure you get one that is for your year car. I think there is a difference between the 97-98 vs the 99-02 vs the 03... but I'm not completely sure which years fit what... but they do mount different on different years

    The things you are describing are the exact same things that I was dealing with
    2005 IBM Pontiac GTO, Built 4.8L .84 Twin Turbos
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  16. #16
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    Default Re: P0121 & poor performance after dyno tune

    Is the MAF sensor descreened? Have you ever cleaned your MAF sensor?

  17. #17
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    Default Re: P0121 & poor performance after dyno tune

    Also check your tranmission fluid. Is the fluid low or does it look burnt? When was the last time the fluid was changed? Does the car shift hard or does it feel like it's missing a gear?

  18. #18
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    Default Re: P0121 & poor performance after dyno tune

    I had the trans filter and fluid changed 2 weeks ago. As a matter of fact it was 2 days before the tune. I havent checked MAF yet but i will. My mechanic suggested cleaning the MAF as well. We rode around yesterday with the tech2 and finally duplicated the problem. it took 30 minutes of real aggressive driving to make it happen. at 90mph cruising, just barely touch the gas and it shifts to 2nd @ 5500 rpm. It would never downshift to 3rd no matter what, would always go to 2nd. when not accelerating and at any mph, the trans was 1 gear lower than it should be. Stop turn the car off and it runs good again. I was about to not worry about it to much because it took driving like a mad man to make it happen, and i never drive like madman..........
    Then today leaving work it happend 5 minutes after driving. I was driving like an old lady cos i was low on gas. Looks like i'll drop the factory PCM back in, Re-install the factory airbox, try to find a black SC pulley, and then try to take advantage of my extended warranty. Thats if the MAF checks out ok. Also i just threw p0130 o2 sensor circuit malfunction.
    Last edited by nugzo; 05-14-2009 at 08:11 PM.

  19. #19
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    Default Re: P0121 & poor performance after dyno tune

    did you get the problem fixed i have a 99 gtp and i had a p0122 code replaced the sensor. problem fixed a week later code came back and i replaced it again. all went fine until yesterday i got a po121 pending code and i cannot figure out the problem any ideas?

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