Back and forth movment when let off throttle.
#1
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Back and forth movment when let off throttle.
Here's the situation.
If I'm cruising down the road, and start going down hill, when I fully let off the throttle the car bucks back and forth in a rhythm and theres a slight knocking noise. It's not violent or anything, but I wanna know whats wrong. If I push in the clutch than it goes away, until I let the clutch out again. So its something in the drive train.
If I just keep it at a steady throttle it doesn't do it, only when I'm completely off the gas.
It's just annoying, and I hope it isn't a serious issue. I can live with it, I just wanna make sure that it isn't a bad thing.
Any idears?
If I'm cruising down the road, and start going down hill, when I fully let off the throttle the car bucks back and forth in a rhythm and theres a slight knocking noise. It's not violent or anything, but I wanna know whats wrong. If I push in the clutch than it goes away, until I let the clutch out again. So its something in the drive train.
If I just keep it at a steady throttle it doesn't do it, only when I'm completely off the gas.
It's just annoying, and I hope it isn't a serious issue. I can live with it, I just wanna make sure that it isn't a bad thing.
Any idears?
#3
82, 83, 88, 82 RX-7again!
Here's the situation.
If I'm cruising down the road, and start going down hill, when I fully let off the throttle the car bucks back and forth in a rhythm and theres a slight knocking noise. It's not violent or anything, but I wanna know whats wrong. If I push in the clutch than it goes away, until I let the clutch out again. So its something in the drive train.
If I just keep it at a steady throttle it doesn't do it, only when I'm completely off the gas.
It's just annoying, and I hope it isn't a serious issue. I can live with it, I just wanna make sure that it isn't a bad thing.
Any idears?
If I'm cruising down the road, and start going down hill, when I fully let off the throttle the car bucks back and forth in a rhythm and theres a slight knocking noise. It's not violent or anything, but I wanna know whats wrong. If I push in the clutch than it goes away, until I let the clutch out again. So its something in the drive train.
If I just keep it at a steady throttle it doesn't do it, only when I'm completely off the gas.
It's just annoying, and I hope it isn't a serious issue. I can live with it, I just wanna make sure that it isn't a bad thing.
Any idears?
Now I drove an SE that was real loose in the back end and it bucked horribly even under power. I would stop driving THAT if it were my car and it bucked under load to find out exactly what was lose/worn. Yours sounds like what mine have been, fairly normal (in my sample of 3).
The Doc has give you some suggestions that of course are right on the money.
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Could it be my timing? Cause I have my vac advanced hooked up to a nipple on the intake manifold, and I was told that that is the wrong place to hook it up.
The nipple in the intake manifold is getting full vacuum at idel.
The nipple in the intake manifold is getting full vacuum at idel.
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#9
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I'll disconnect the vacuum line and take it for a spin tomorrow to see if that solves it. There is a nipple on my Weber that is specifically for vac. advanced, Ill hook it up to that...or lock my dizzy.
#12
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Mine does it too i have a 85 GSL bone stock, new fuids, filters, plugs only 130K on it. It happened to me on the dyno i was in 3rd when at about 3K and holding the gas steady, when it just started bucking VOILENTLY! and almost fell off the machine. We then put tie downs and tried again but to avail it did the same thing, tried giving it gas, just got worse and died, even when i got on the clutch it died. then it wont start for about 20-30 minutes then will start up like nothing wrong till i reenact that moment. and for the record it did it in 2nd and 4rth so gear doesnt matter. i already tried a new fuel filter, and nothing. new tank nothing, pump nothing. im running out of ideas besides the carb. or a spark problem i heard maybe the coils. it has been sitting for 12 years.
#14
I think it has to do with the shutter valve that controls the idols as you let the gas go. Mine was doing the same thing. I replaced the shutter valve and it stopped jerking back & forth once you let the gas go.
#16
Don't Cross The Streams..
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ive driven plenty manual cars and they are NOT supposed to buck like mines did! it was jerking to pieces. best way i can describe it is like a shark attack, thrashing back and forth.
Last edited by Rotor_Venom08; 05-13-09 at 08:40 PM.
#17
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You're missing the deceleration dashpot on the carb. It lets the throttle close slowly to avoid backfire, and to a lesser degree, what you're experiencing.
#18
Don't Cross The Streams..
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okay but to my knowledge i wasn't decelerating i was holding my foot steady on the gas, maybe accelerating if anything. how would i know? if something was missing? i know my carb needs a rebuild because its 12 years off the road, and my choke cable get stuck open its all rusty. I though of you actually due to the recommendations from the masses. Ill PM you.
#19
Sleeper but still slow
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Mine does it, it seems carb related to me. I'm running a Dellorto DHLA though, don't know if it's a property of that. It's like someone aove described, coasting in gear, off the throttle, but only when I'm near idle. Like under 2,200 RPM like 30MPH in 5th, etc.
#20
Waffles - hmmm good
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It might be two things; the motor and tranny mounts are old and worn and when
you use the engine as a brake (which is whats happening when you let off the gas
and keep it in gear) it may buck a bit because of slight differences in compression on
the rotor faces (just my little theory) or its caused by the vacuum advance being
hooked to the intake like Trochoid said.
I have it that way on my Dell and if I get it in just the right spot off idle I can make it
buck like this at will but its easy to control. I know I'm not supposed to use straight
intake vacuum on the advance so lets not debate it but it really makes a huge drivability difference other than this small issue. If the Dell had a real advance nipple I would use it.
you use the engine as a brake (which is whats happening when you let off the gas
and keep it in gear) it may buck a bit because of slight differences in compression on
the rotor faces (just my little theory) or its caused by the vacuum advance being
hooked to the intake like Trochoid said.
I have it that way on my Dell and if I get it in just the right spot off idle I can make it
buck like this at will but its easy to control. I know I'm not supposed to use straight
intake vacuum on the advance so lets not debate it but it really makes a huge drivability difference other than this small issue. If the Dell had a real advance nipple I would use it.
#22
weak minds wear the crown
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It might be two things; the motor and tranny mounts are old and worn and when
you use the engine as a brake (which is whats happening when you let off the gas
and keep it in gear) it may buck a bit because of slight differences in compression on
the rotor faces (just my little theory) or its caused by the vacuum advance being
hooked to the intake like Trochoid said.
I have it that way on my Dell and if I get it in just the right spot off idle I can make it
buck like this at will but its easy to control. I know I'm not supposed to use straight
intake vacuum on the advance so lets not debate it but it really makes a huge drivability difference other than this small issue. If the Dell had a real advance nipple I would use it.
you use the engine as a brake (which is whats happening when you let off the gas
and keep it in gear) it may buck a bit because of slight differences in compression on
the rotor faces (just my little theory) or its caused by the vacuum advance being
hooked to the intake like Trochoid said.
I have it that way on my Dell and if I get it in just the right spot off idle I can make it
buck like this at will but its easy to control. I know I'm not supposed to use straight
intake vacuum on the advance so lets not debate it but it really makes a huge drivability difference other than this small issue. If the Dell had a real advance nipple I would use it.
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