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Thread: Throttle Issue

  1. #1

    Default Throttle Issue

    Hi there. Just put a Sniper on my 383 LT1 Chevy to replace the carby I had. Everything is great, car fired straight up and idle is nice & smooth. The issue I have is intermittent spiking of the throttle. With the ignition on, when I press the accelerator, the TPS appears to read just fine, but when I start the car and press the throttle in park, it appears to read incorrectly. It's like it struggles to get over 10%. What is more concerning for me, is that on the initial drive, the car went to 3000 RPM in gear with a light touch of the pedal and wouldn't return. Then when looking at in the garage, I found my accelerator adjustment bolts loose. Did them up, retested in park and with a light touch of the throttle, the car went wide open throttle. If this had happened when driving, it would of been a disaster. I'm new to EFI, so I'm not sure where to start. The system has about 3 KMS on it, but surely this isn't a Learn issue. Can anyone point me in the direction of where to start? Much appreciated. Scott

    Sorry, I should also add - it does the same thing with the throttle cable disconnected and manually operating the accelerator. Bad TPS out of the box?

  2. #2

    Default

    I just installed the Sniper EFI on my 383 also. It kind of did the same thing you're describing until I adjusted the IAC. It's the little hole on the top of the throttle body. Plug it with your finger while you adjust the idle screw 50 RPM below your Target Idle Speed. Try that and see if it works.

  3. #3
    Join Date
    Dec 2009
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    Connecticut
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    Default

    Good advice. FYI: The Sniper EFI doesn't have the same TPS Autoset function as the Terminator, HP & Dominator ECUs. The Sniper EFI calibrates the TPS sensor at every key-on event. If replacing the TPS:
    The TPS sensor is located at the end of the primary throttle shaft, opposite end of the throttle lever. It's slotted, so install it in the same position. Holley 543-111 TPS or Standard Motor Products TH191 TPS.
    http://forums.holley.com/showthread....=2760#post2760 (Replacement Sensors For Holley EFI - Auto Parts Store)

    Sniper EFI Idle Setting/Throttle Blade Setting (Holley Sniper EFI Quick Start Manual):
    Once the engine is up to operating temperature, the idle speed can be set to what was configured in the Wizard.
    To do this, open up the Initial Startup gauge screen that was used in section 17.0. With the vehicle in neutral,
    adjust the idle screw until the IAC Position reads between 2 & 10%. While adjusting the idle speed screw, if the
    TPS Position begins to read higher than 0%, cycling the ignition switch will recalibrate the TPS back to zero.
    NOTE: Do not attempt to set the Target Idle Speed and IAC Position until the engine is above 160°F!
    http://documents.holley.com/199r11193.pdf (Holley Sniper EFI Quick Start Manual - "Idle Setting/Throttle Plate Setting", Page 12)
    https://forums.holley.com/showthread...-Idle-Solution! (Sniper EFI High Idle Thread)
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  4. #4

    Default

    Throttle return springs?

  5. #5
    Join Date
    Dec 2009
    Location
    Connecticut
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    Default

    Or the secondary throttle blades not always fully closing?
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  6. #6

    Default

    Thank you Malibu & Danny. My idle I think is set correctly. At operating temp, the car is idling around my set target of 850 RPM and the IAC is jumping around, but pretty much between 5-9%. A couple more questions if I may. I’m assuming that the car revving as hard as it did the second time, must be stuck open butterflies. Is there anything in the system that could cause it to rev the way that it did? I just want to rule out that it's electronic. As I said in my original post, the TPS seems to be a lot less sensitive when the ignition is on, then really supper sensitive when the car is running. Again, is there any reason for this that you know of?
    Last edited by Blkace32; 02-20-2018 at 03:18 AM.

  7. #7

    Default

    Hi Danny, you were right, the secondary throttle blades are sticking. Seems to be in the actual throttle body itself, just catches on the link. Can I ask if you know what the fix is for this?

  8. #8

    Default

    If it's the blades sticking, then you loosen the screws & recenter them. If it's the return spring for the secondaries, you take it apart to tighten the spring one turn. If it's the little tab that kicks the secondary closed, you bend it out some more. You do not use any grease or oil on the linkage.

  9. #9
    Join Date
    Dec 2009
    Location
    Connecticut
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    Default

    Quote Originally Posted by BITE_ME View Post
    If it's the return spring for the secondaries, you take it apart to tighten the spring one turn.
    If this is the problem, the secondary coiled shaft spring can be tightened one additional turn without disassembling the throttle body. I've even done it with the throttle body on the engine.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  10. #10

    Default

    Thanks all, greatly appreciated.

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