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Erratic Engine Speed between 2000-2500 RPM
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BBOB
New User
Aug 31, 2006, 1:29 AM
Post #1 of 2
(2803 views)
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Erratic Engine Speed between 2000-2500 RPM
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My 2000 Pontiac Grand Prix GT has started surging 500 RPM once the car reaches 2000 RPM. The surging lasts anywhere from a few seconds to several minutes. It will stop if I accelerate once it starts. Problem occurs with cruise control on also. The problem does not always occur as I reach 2000 RPM but it does seem to be happening more frequently as time goes by. Very annoying as the car physically lunges when this occurs. What can be the cause???
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DanD
Veteran
/ Moderator
Aug 31, 2006, 5:59 AM
Post #2 of 2
(2791 views)
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Re: Erratic Engine Speed between 2000-2500 RPM
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TPS (throttle position sensor), MAS (mass air flow) sensor, VSS (vehicle seed sensor, TCC (torque converter clutch) and not doubt a few other sensor or working devises that are controlled and monitored by the PCM (power train control module) (computer); anyone could be causing this. A sensor or devise may just be starting to fail but is still running within its perimeters and the PCM won’t set a code.
All of which may need to be tested or monitored with the use of a scan tool. A scan tool that is capable of capturing what is call a “snapshot” of the sensor inputs and the commands that the PCM has given to a working devise.
A snapshot is like taking a number of still pictures (average being 120) of all monitored engine performance devises and sensors activity. These snapshots can be downloaded to a PC at a later time and examined at a much slower rate. One frame at a time if need be, looking for glitches that in real time would go unnoticed. The rate of information transfer is so fast that a 60 snapshot event would be over in less then a second.
The operator of the scan tool would set up the scan tool to record a snapshot event, drive the vehicle. When the problem occurred; the tech would begin recording the event by pressing a button on the scanner like you would on a video camera to record your images.
Most scanners can be calibrated that it will take a number of snapshots immediately before and the same number after the button was pressed on the scanner. Doing this will give you baseline information of things running “normally” and then hopefully you will see what changed to cause the surge.
Sorry for being so long winded but I didn’t know how else to explain a snapshot; also that a good quality scanner has a lot more uses then just reading codes.
After saying all of this; there are also non-electronic things that could be causing this. Such as worn/loose timing chain a slipping transmission ect; so a complete inspection would be needed to begin diagnosing this.
Dan.
Canadian "EH"
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