How do you really know that it is running lean?  Have you monitored the O2
sensor output while the problem occurs?  If there is a lean condition, I
would expect the O2 output to stay low rather than bouncing up and down as
it should.
  You didn't mention any checks of the Hall sensor signal/circuitry.
 Things sometimes vibrate strongly only at certain frequencies (resonate).
 Maybe this is happening to some wire that has a poor/intermittent
connection.
   A very thorough check for vacuum leaks might also be a good idea.

Good luck,
Larry A.

On Wed, Nov 20, 2013 at 7:08 AM, jf kulina <redbluephish@hotmail.com> wrote:

> "BlueJean" my 4 speed '90 MV with 146,046 miles and stock 2.1 in her,
> keeps running lean at around 2500 rpm in neutral or on the highway.  The
> engine will
> "jerk" quite noticeably until I mash the accelerator or push the clutch
> in (when going down the road).  The following test's/possible solutions
> have been done by my very competent but stumped mechanic:
> Compression test  - 135 - 155.
> Coil/spark plug resistance test.
> Fuel pressure test at test tab - idle - 32. under load - 36.
> ECM pin out scope for:  Collant temp; Air flow; Injector output; Air
> intake;
> O2 sensor voltage; Emission input and Idle switch test.
> Swapped ECM and Air Flow Meter for known good.
> Sealed exhaust leak.
> Replaced all grounds for ECM on left cyl head and under ignition coil.
> Swapped Digifant control relay with fuel pump relay.
> Drained fuel and found 10% alcohol in fuel.
>
> Any thoughts for solutions would be REALLY appreciated...
>
> Thanks,
> John Kulina
>