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I recently noticed that when coasting or breaking is followed by acceleration (seems to be only when the car is moving between 25 and 40 mph) that there is a slight jerk. After recreating the problem a few times I noticed that the rpms jump up to just a little over 2000 then after the jerk it drops back to 1000-1500 which is usually normal. While it hasn't happened every time these conditions are replicated, it has been fairly constant. Hoping that it would be an easy fix, I just had the transmission fluid flushed. The car is at a little over 100k miles. Transmission is automatic. Any thoughts on what the trouble might be?

Observations that I haven't been able to confirm yet: It seems like the problem occurs less going uphill (haven't tried recreating the problem going down hill); It also seems like the longer periods of driving (15+ minutes) result in less occurrences though I'm not certain of this either yet.

UPDATE: I have noticed that when I take my foot off the gas between 25-35 miles per hour the RPMs drop down to just over 500. At any other speed it remains over 1000. If I begin accelerating before the RPMs drop below 1000 at the speeds where I'm having this issue it doesn't seem to jerk but if I let it drop below 1000 it does. Does this change the circumstances at all?

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Is it worse when the engine is cold? –  Nick Jul 29 '12 at 12:26
    
by cold do you mean when the car has sat for a long time (say over night) or do you mean physically cold? If you mean sat for a long time not running then possibly yes... I haven't been able to confirm that yet though this is something I've considered. If you meant physically cold I have no way of knowing that right now because it just started a couple of weeks ago and we've had warm weather the entire time. –  Kenneth Jul 29 '12 at 13:20
    
yes, when the car has cooled of completely to ambient temperatures. –  Nick Jul 29 '12 at 15:01
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Is there a check engine light on by chance? Also, out of curiosity where was the "transmission flush" performed and what was included in the flush? –  cinelli Mar 22 '13 at 17:23
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@EricFossum converter lockout clutch would be felt at coasting speeds as well as slight uphill acceleration... –  cinelli Mar 22 '13 at 17:25

1 Answer 1

You could be driving it incorrectly. An automatic transmission will switch at lower or higher RPM's depending on how hard you're pressing the gas pedal. A gas pedal is actually an air pedal. It forces more air conduction by opening the throttle body, located between your intake manifold and air filter(or cold air intake). If you suddenly push the gas pedal down while going 20 mph, at 4,000 rpms, then the second you hit 6,000 and your car shifts, you're going to feel a jerk. If you ease off the pedal, your car will switch gears at a lower rpm, as high torque is closer to around 2,500 rpms depending on the gear, and it will give you better gas mileage. In order to accelerate faster, as your transmission knows, you must reach high RPM's and with that, when you switch gears, it will pick up at a relatively higher RPM than if you were accelerating slowly.

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