'89 S10 4.3 erratic idle speed

[76C10Stepside]

My recently acquired 1989 S10 with 4.3 Vortec engine and A/C idles funny.
When first started up, it idles very fast for about 30 seconds or so, then slows down, but for the first minute or so of driving, the idle speed keeps stepping up and down. It also steps up and down constantly when idling, but drives just fine. It sounds like the A/C is engaging/disengaging when the idle speed changes. The graphical tachometer stays at the 750 mark with no visual indication that the idle is stepping up, maybe it's just because the resolution is so low (looks like 250 RPM increments, but will have to check next time I drive it).

I haven't tried reading the error codes from the ECM yet, no shop manual, but guessing it's like my '87 Buick, where you jump two pins on the panel after disconnecting/reconnecting the battery to reset codes and start the engine to register any new codes.

Thinking it's either a dirty or bad mass-airflow sensor or a problem with the A/C. Or is this "normal"?