Sometimes TQ problems can cause shudder.  Or maybe a bad mount?  CV joint?

If it feels like the engine drops a cylinder under load, I would suspect an
ignition problem.  You can check the wires for arching in the pitch dark and
mist them with a spray bottle to stress test them.

One way to isolate a specific cylinder misfire is to disable each cylinder
one-by-one and see if the problem gets worse.  If it doesn't, that's your
dead cylinder.  Of course on a 4 cylinder engine, this means your running on
2 cylinders sometimes.  This could be problematic on a rolling test so do
your testing in a traffic-free area.

Or wait for better advice from someone else :)

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
John Rodgers
Sent: Wednesday, September 24, 2014 8:41 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Engine Shudders -2.1L WBX.

I have a 1991 Carat with auto tranny. On floorboarding to go up a hill or
kick down into a lower gear to pass, the  engine seems to drop a cylinder
an shudder as if not firing. I have a Shoebox Electronic ECU Monitor hooked
up and have the engine fine tuned and all the numbers are good and the
lights are correct, yet I get this shudder anyway. I checked with an
induction timing light the firing of  each ignition wire up 2500 rpm. Each
was good. Yet it still shudders on pressing the pedal to the metal.

Any ideas?

John the Gimp