Thread: Rpms drop when I stop excelerating and let off the gas

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  1. #1 Rpms drop when I stop excelerating and let off the gas 
    bbfanatic23
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    Default 10-25-2012
    I'll be driving down the road going from 0 to 45mph and as soon as I stop accelerating the speedometer will drop to 0 and go haywire going back and forth between my speed and 20 and 0 and 33 and so on. As soon as I let off the gas I can feel what seems like a rough downshifting. My car also has some pretty rough shifting. I've replaced the pcm and that did nothing.



    The following is a conversation I had with someone on the chat about my replacement pcm that might get yall up to more up to speed on whats going on. The conversation starts at the bottom of the page...

    25/10/2012 6:21 PM bbfanatic23 thats what i need to know... but if thats pretty much true then i think i got a bad pcm
    25/10/2012 6:20 PM bayus2972 best bet for you is to post this in a thread...let the whole forum gang voice in....most are WAAAY more knowledgeable than I...
    25/10/2012 6:20 PM bbfanatic23 so if your wiring harnest gets shorted out wires then its frys the pcm basically everytime?
    25/10/2012 6:19 PM bbfanatic23 i gave him my vin
    25/10/2012 6:19 PM bbfanatic23 i didnt 'reset' it because i never got that far because it started up right away.
    25/10/2012 6:18 PM bayus2972 someone jump in here..aren't PCM's suppose to be VIN programmed?
    25/10/2012 6:18 PM bbfanatic23 but...
    25/10/2012 6:18 PM bbfanatic23 ya couse i got instructions on reseting it just like the dealer would
    25/10/2012 6:17 PM bayus2972 that's when I found the wire rub...took it back and they fixed the wires...but the PCM was fried
    25/10/2012 6:17 PM bbfanatic23 maybe i got a bad one...
    25/10/2012 6:17 PM bbfanatic23 thats crazy... its got to be my pcm
    25/10/2012 6:17 PM bbfanatic23 wow really?
    25/10/2012 6:16 PM bbfanatic23 but people are saying that thats a last resort and its prob not the pcm
    25/10/2012 6:16 PM bayus2972 yep..as soon as I picked up the car (from a previous shop job) I test drove it and it did the same thing you described....let off the gas, speedomoieter goes haywire and the car jumps down a gear..
    25/10/2012 6:16 PM bbfanatic23 Im just confueed because the issues that ive had/ having make it seem like its the pcm..
    25/10/2012 6:15 PM bbfanatic23 so what same problems as me were you having?
    25/10/2012 6:14 PM bbfanatic23 I see... but you said you were having the same probs as me?
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  2. #2 Re: Rpms drop when I stop excelerating and let off the gas 
    Fivefingerdeathpunch
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    Default 10-25-2012
    That is very odd.

    I wonder if the VSS can cause this problem.

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  3. #3 Re: Rpms drop when I stop excelerating and let off the gas 
    Toms04compg
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    Default 10-26-2012
    That happened on my 04 once... Very weird , Keep us posted.
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  4. #4 Re: Rpms drop when I stop excelerating and let off the gas 
    Erik Adam Rodriguez
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    Default 10-26-2012
    check pcm connection maybe use some dieelctirc grease on the connectors
    02 grand prix gt- L67 swap, ZZP 1.0 pcm, thrasher CAI, SLP 2.5 catback, A/C delete, 02 emulator, poly dog bone mounts, 6000k projectors with CCFL halos, 12 in slotted front rotors, ported blower and intake, evap and EGR deleted, 12" kicker cvr with 1000 watt amp, alpine cda 9886 deck
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  5. #5 Re: Rpms drop when I stop excelerating and let off the gas 
    acidcrashdburnd
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    Default 10-26-2012
    My moms car did this, Changed the speed sensor.. I believe and it went away.
    2005 GPGT- Top Swapped Click me! 15.5 @109
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  6. #6  
    bbfanatic23
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    Default 10-26-2012
    VSS? Speed sensor hard to get to? Thanks guys!
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  7. #7  
    bbfanatic23
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    Default 10-26-2012
    Anybody know if the PCM has a built in power supply to where I would need to unplug it for a extended amount of time before I can try and reset it?
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  8. #8 Re: Rpms drop when I stop excelerating and let off the gas 
    WolvesSoulZ
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    Default 10-26-2012
    When mine did that it was my VSS, it was badly plugged in. But it caused the same thing, and the transmission did erratic shifting.

    It's the VSS for sure, in my opinion / experience. Change the VSS or Check if it's plugged in good.
    2000 GT - L67 swapped SOLD | 2004 GT1 - Winter Beater - SOLD
    2004 GTP Comp-G - 3.3"/3.2", XP, #50 , 4" MAF, SD's, 180*, AL103's, HAI, Tuned, 06+ Dual pistons brakes, STB's, SSC's and FE3.
    2011 Audi A6 S-Line - Also Supercharged
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  9. #9 Re: Rpms drop when I stop excelerating and let off the gas 
    bbfanatic23
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    Default 10-27-2012
    My repair manual is at my parents house. Any idea of the location/ how easy it is to change it?
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  10. #10 Re: Rpms drop when I stop excelerating and let off the gas 
    WolvesSoulZ
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    Default 10-27-2012
    The VSS is on the passenger side of the car, jack the car, remove the wheel, you'll see the transmission differential (where your axle shaft goes in), it's the sensor above. Easy to find. It's held with a bolt or two, don't remember.
    2000 GT - L67 swapped SOLD | 2004 GT1 - Winter Beater - SOLD
    2004 GTP Comp-G - 3.3"/3.2", XP, #50 , 4" MAF, SD's, 180*, AL103's, HAI, Tuned, 06+ Dual pistons brakes, STB's, SSC's and FE3.
    2011 Audi A6 S-Line - Also Supercharged
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  11. #11 Re: Rpms drop when I stop excelerating and let off the gas 
    bbfanatic23
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    Default 10-27-2012
    Sweet! I'll check it out. hopefully that's my problem. Thanks for the help!
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  12. #12  
    bbfanatic23
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    Default 10-30-2012
    That was the problem. Bad connection before the sensor at two of the wire's couplers. Thanks for the help guys. I'm good with body work and paint. So let me know if y'all ever need any help in that area.
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