Scroll down to page 80 in this PDF
http://www.startekinfo.com/StarTek/outside/12264/Program/Engine/103/07.3-0121.pdf
There you will find this picture
This shows the position of the parts for the 1988 and 1989 models.
If you unhook "N3" then you should be able to get the engine to run with a high idle of about 1500 rpm. All of the CIS interference will be removed from the equation. If the engine still surges then I guess you need to be looking at parts of the car that are not CIS related.
Around that area in the PDF (page 80) you can also find the position of the sensor (as w123fanman says) behind the steering wheel as well as the connector position behind the dashboard.
If you can't get codes from "X92" then you need to measure the error codes from the duty cycle via "X11" and then the information given before page 80 in the PDF linked above becomes relevant.