Check your oxygen sensor and oxygen sensor wiring.  The clues
are that it gets better when you turn the engine off and also
at full throttle.  Wiring:  the wire to the ECU is shielded and
the shielding can poke through the signal wire and short it.

Plug a digital voltmeter into the connector from the oxygen sensor on
the left side of the engine bay and see if the voltage is oscillating
between 0-1 volt.

tabe johnson/87 westy