Most likely the jerk you are experiencing is due to the engine going rich,
not lean. This symptom is also part of the famed "Vanagon" syndrome. Mashing
the accelerator closes the full throttle switch which will largely ignore
the O2 sensor. As another test try cycling the ignition switch. If the
problem goes away for some period then the problem is related to the O2
sensor system. The most important ground is the one in the harness to the
distributor. From the factory this was often connected at the base of the
oil breather. Plastic does not make a good conductor.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
jf kulina
Sent: Wednesday, November 20, 2013 7:09 AM
To: vanagon@GERRY.VANAGON.COM
Subject: '90 MV running lean at 2500rpm

"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