Car jerks after while accelerating after 40mph - Mazda Forum

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Old 09-19-2007, 12:14 AM
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Hey,

Am lookign for some input.
At about 40 mph, my car starts jerking when I accelerate.
It does it off and on.
Any ideas?

Clarification
Yeah, what it does is if I go past 40 then let it deaccelerate down to like 36 and then try to accelerate again, I get a jerking movement everytime I try to accelearte. It doesn't just jerk once then accelerate smoothly, it is a continuous jerk like the car loses power than accelerates then loses power than accelerates. and it continues cfrom like 40 -60 mph. I hope that is a little clearer.
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Old 09-19-2007, 12:24 AM
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If its when upshifting after just downshifting my car does that too sometimes but not really hard jerking. After the tranny fluid flush it got a little better.
-Steven
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Old 09-19-2007, 12:52 AM
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Under light throttle, mine kind of jerks slightly sometimes like it's alternating between coasting and engine braking. I figure it might be a badly adjusted TPS or maybe the sensor itself is worn or tracked.
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Old 09-19-2007, 02:34 PM
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Yeah, what it does is if I go past 40 then let it deaccelerate down to like 36 and then try to accelerate again, I get a jerking movement everytime I try to accelearte. It doesn't just jerk once then accelerate smoothly, it is a continuous jerk like the car loses power than accelerates then loses power than accelerates. and it continues cfrom like 40 -60 mph. I hope that is a little clearer.
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Old 09-19-2007, 03:19 PM
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How much throttle do you apply? Did you try full throttle? If not try it. Does TCS flash while jerking?

And what year trim mileage?

Quote:
Yeah, what it does is if I go past 40 then let it deaccelerate down to like 36 and then try to accelerate again, I get a jerking movement everytime I try to accelearte. It doesn't just jerk once then accelerate smoothly, it is a continuous jerk like the car loses power than accelerates then loses power than accelerates. and it continues cfrom like 40 -60 mph. I hope that is a little clearer.[/b]
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Old 09-19-2007, 03:33 PM
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If it's the same as mine, the jerking goes away once you press the accelerator a little further. It only happens when the throttle is barely pressed (like slow acceleration above 45mph) or accending a very slight grade at a constant speed. The throttle sensitivity on the miller cycle is such that driving normally requires very small throttle inputs to keep from lurching forward. In comparison to the 2.5L, it's on the opposite end of the spectrum requiring large input for small changes in acceleration at some speeds. I was thinking that the TPS is sending erratic output to the ECM when it is in that almost closed position or the closed throttle position sensor is sending "open----close-open-------close-----open" causing the jerking. No way to tell for sure until you (and I) drive with an OBDII data logger and monitor the TPS and CTPS output while the jerking occurs.
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Old 09-19-2007, 03:35 PM
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Quote:
How much throttle do you apply? Did you try full throttle? If not try it. Does TCS flash while jerking?

And what year trim mileage?[/b]
Have not tried full throttle. Will try it. TCs does not flash..

It is a 99 L 98,000
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Old 09-19-2007, 04:45 PM
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I have same the same issue with my ride. I am wondering what it is as well. I have no CEL and the traction control does not come on either. I am leaning towards something to do with the fuel system....
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Old 09-20-2007, 11:34 AM
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Quote:
I have same the same issue with my ride. I am wondering what it is as well. I have no CEL and the traction control does not come on either. I am leaning towards something to do with the fuel system....[/b]
That's why I'm thinking that it might be something with the TPS or CTS. When your foot comes off the accelerator at speed, the fuel injectors switch to a 0% duty cycle. If the ECM *thinks* the accelerator isn't depressed (when it really is if only slightly), it cuts fuel and causes a mild jerk. My dad had a mid-90s 4-cylinder Camry years ago that did the same thing and we never figured it out. The only things I can think of are a bad CTS or a TPS with erratic output voltage throughout its range or within a small portion of its range.

Erratic TPS output can also cause the automatic transmission to shift abruptly every now and then depending on throttle input. The ECM really depends on accurate TPS readings to smooth the shift shock between gears. My transmission shifts smoothly for the most part, but every now and again, a light throttle 1-2, or 2-3 shift will make the car buck a bit. All the more reason to blame the TPS I suppose.
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Old 09-20-2007, 01:04 PM
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This also means it consumes no fuel when cruising (fast enough). Thats why i let it slow down itself by just releasing the accelerator when exiting highway, if traffic allows.

Quote:
When your foot comes off the accelerator at speed, the fuel injectors switch to a 0% duty cycle.[/b]
I wonder if the TPS can be cleaned/serviced? Apperantly the idle signal in the picture below may dominate over throttle valve opening signal for small inputs..

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