Hey Neal,

Do you have access to a Bentley manual?  I had a similar symptom set when I
first got my 88 GL, and it just about drove me nuts. Ken Wilford of
vanagain.com gave me a tip about the wiring between the O2 sensor and the
ECU: the signal voltage from the sensor is carried by a coaxial cable (like
a RCA cable for you stereo or TV at home). Voltage on the inside, then
insulator, then a copper shield, then outer sleeve. If the the cable
deteriorates to the point that there's any continuity between the inner
conductor and the outer shield, the ECU will lose it's mind, more or less.

Page 24.62 of the Bentley manual has the details, but you'll be checking
with an ohmmeter between pins 2 and 13 of the big connector at the ECU. With
the O2 sensor connected, there should be no continuity between them.

On the same page, there's a test for the throttle switch, too. Could be
worth checking.

Good luck,

Matt Sutton
Brooklyn NY
88 GL