so this truck (from the serial number) is the s15-g system, your best bet is to bite the bullet and call the Cat or Mitsu dealer, and tell them you will need the persons that know how to set up an accel pot with the laptop in this version [s15-g] truck.
you might first make sure nothing has gotten tied into any of the wires that feed into the circuits monitored by the ECU. Usually this truck will only low idle [650rpm, normal idle is about 725/760] if their is an abnormality.
after you are sure the wires are 'clean' you might try a 'known good' ecu.
on this truck, there is a 'fuel trim' [vacuum control solenoid valve] with a red and white wires. DO NOT TEST these wires WITH A METER with the ECU connected.