Car runs great, except for one little quirk.  While driving at highway speeds, 60-70mph, if I let off the excelerator there is a quick jerk that scares the heck out of the passenger.  (I know I'm letting my foot off the gas, but the passenger doesn't)  I was told the problem may be in the drive train so had that all gone thru - twice - and still no dice.  Problem still exists.  Also checked the vaccum advance and it made no difference.  Anyone else having this type of problem? 

 

Jerk forward or backward?  What RPM?  Stock 280Z EFI, all parts intact?  Could be fuel cut at 2800 RPM.

jerk backward.  about 2000 rpm?, stock EFI, all parts intact. 

Dash pot rod may need adjustments. The white plastic thing with an open hole that looks like there is hose missing.

Or maybe the BCDD?

Is the drive train original?

 

Standard or auto?

 

Gone thru twice meaning what exactly? 

The differrential has been take out and checked to match correct specifications.  Standard transmission.  Tell be about the BCDD.

Here's when I was fooling with mine, http://www.classiczcars.com/topic/42497-bcdd-removal/

 

You could pull the wire off the solenoid to disable it and see if has any effect.  

jerk backward.  about 2000 rpm?, stock EFI, all parts intact. 

2,000 RPM sounds too low for 60 or 70 MPH. Double check that RPM. If it's anywhere near 2,800 RPM ( + or - 200 RPM ) it could be just the Fuel cut...which is perfectly normal. How bad is the jerk? Unless it's really big, best solution may be to find another passenger who's less " nervous "...

 

Seriously, could also be the BCDD as previously mentioned.