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Thread: Car accelerating without touching the throttle.

  1. #21

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    OK, so I've done more checks. Motor mounts look good. Throttle cable is clear of any obstruction. Checked all the IAC settings. Tried driving with the kickdown cable disabled. And it's still doing the same thing, I'm completely stumped. Is there any way the Sniper can hold the throttle engaged in the same position for a few seconds?

  2. #22
    Join Date
    Dec 2009
    Location
    Connecticut
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    20,517

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    Quote Originally Posted by gdbst1 View Post
    Is there any way the Sniper can hold the throttle engaged in the same position for a few seconds?
    Not the actual throttle lever, but it can raise the idle speed RPM. What's your IAC Hold Position % set to? What's your IAC Ramp Decay Time (sec) set to?
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  3. #23

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    I've tried adjusting both of those to 0 and it didn't make a difference. It's definitely holding down the throttle, I can see it release the accelerator pedal and the throttle position is up around 40-50%.

  4. #24
    Join Date
    Dec 2009
    Location
    Connecticut
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    20,517

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    Then one of the throttle shafts or blades is sticking in the bore(s). Remove all linkage/cables from the throttle body and work the throttle lever by hand.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  5. #25

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    This will sound like a bad idea at first, but this is how I found my problem. Chock the front tires and open the hood so you can actually see the engine from the drivers seat. Then try to power brake it, but not to the point of spinning the tires. If you see any up or tipping movement it’s a bad motor mount. I had the exact same issue you do. I checked the mounts and they looked good. I did the same thing except my truck is a stick so I had to do a couple launches in my driveway with the hood up to see it. It sounds sketchy, but it works if you're careful about it.

  6. #26

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    GDBST, what "checks" did you do to rule out the motor mount? When you said you have a throttle cable, it made me much less suspicious of the motor mount. It's the throttle rod that gets in a bind and sticks when you have a broken motor mount. Cables not so much. But everything else you describe sounds exactly like a broken motor mount. You wouldn't be able to see the break just by looking at it in the car. You have to do the power brake test.

  7. #27

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    I've had it at the mechanic and he's assured me the mounts are OK. Here's what I've checked so far:
    Changed the idle IAC to 0%.
    Changed the Hold IAC to 0%.
    Disconnected the IAC.
    Cleared any possible issues that can catch on the throttle linkage.
    Driven it without the air filter.
    Checked the butterflies and they're spotless and move perfectly.
    Disconnected the kickdown cable.

    Sorry, it is a throttle rod not cable. I did notice last night that there is a mark on the side of the valve cover from where the throttle rod bolt is hitting it. There's less than an inch between the two. My guess is when the motor moves it's holding the rod in position until the gear is changed and the motor goes back to position. Very difficult to tell. It's at the shop now, the mechanic is going to try put it on the Dyno and simulate road conditions and see how close it gets. Not sure if I've mentioned it, but it's a '69 Camaro. Has anyone had to modify their throttle linkage/setup at all? Thanks.
    Last edited by gdbst1; 04-15-2019 at 04:38 AM.

  8. #28

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    Sorry to keep coming back to this over and over, but I'm a “test it myself” kind of guy. There are plenty of mechanics out there that miss things, or keep working on it to get more fees. May not be the case here, but please do yourself a favor and test this yourself. It will take two minutes or less. Open the hood, crank the car, hold the brake and give it a little gas. Watch the engine and see if it rises a little? When you take your foot off the gas, but keep holding the brake, does the RPM stay up? Knock it in neutral and see if you see the engine drop and hear a thunk. Until you do this test yourself, you're just chasing your tail.

    My car is a '69 Camaro, with a throttle rod. The modification I had to make when mine did this exact same thing is fix the broken motor mount, LOL. Your engine is moving as evidence by the marking of the valve cover. Even if by some chance it's not completely broken, there is enough slop in the rubber in the mount that it is allowing the engine to move, a lot, so it needs to be replaced.

    Get a solid motor mount and install it on the drivers side and you will have no issues. Leave the rubber based mount on the passenger side and leave the transmission mount as rubber based. If you are adamant about not putting a solid mount in it, then at least get a new aftermarket mount.

  9. #29

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    Well guys, you were spot on. Got the mechanic to check the mount again and sure enough, cracked right through. The motor was lifting and the valve cover was holding the throttle rod in position. All fixed now and running like a dream. He did mention that it might be worth getting some better mounts put on. Any suggestions? Thanks again for all your help.

  10. #30

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    Good thing you were willing to listen to the people on the board. Sometimes the answer is obvious to experienced users even if the OP is saying "that isn't it". You had a potentially dangerous situation so it's good that you did a double check rather than just assuming that it was a Sniper issue.

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