95 Sonata OBD1

Hello folks, not many replys in these posts. Anyone know how to read the obd1 codes with the analog voltmeter specified in the useless Haynes manual? My problem is really rough idle. I paid a mechanic 1,200 to get to idle at 600 rpms 50% of the time as opposed to 3% of the time. First code read I got was MAF which I replaced. Didnt do anything. Mechanic did the whole top end and said he found a valve with a chunk taken out of it. He gave it to me. Runs better but still sucks. I would like to read the new code myself.
Thanks for any assitance in advance.
Jim.