Well, we're making progress.
Jerking can have a lot of causes with different subtle symptoms. A rocking engine can tug on a wiring harness that causes an intermittent connection in a connector terminal and an intermittent cutout of the ignition system or injector. A failing sensor, mostly the MAP sensor, can be supplying an incorrect signal voltage resulting in wrong fuel metering calculations. As long as the signal voltage is within acceptable limits, it won't set a diagnostic fault code, but it usually doesn't take very long for the failure to become bad enough that the Engine Computer does detect a problem and sets a code.
With no fault code, you have to view live data on a scanner to see if something doesn't look right or can provide a clue. Most scanners have a "record" feature that allows you to record a few seconds of sensor data when the problem occurs. Since the data passes through the scanner's memory, the recording actually starts a few seconds before the button was pressed. The recording can be reviewed slowly later to see what changed when the symptoms occurred.
Jerking can also be caused by worn steering and suspension parts. Clues are a sudden pull to one side, or a change in the centering of the steering wheel. The people at tire and alignment shops are experts at finding the causes of those things.
Sunday, July 3rd, 2016 AT 8:59 PM