1.8L engine idles inconsistently between 750-1150 RPMs, even after warm-up?

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1.8L Automatic Trans '92 Acura Integra GS W/168K miles. Tune-up within last 30K miles. Passed prior smog in 2012 at the same shop. Very limited budget, no code check devices, disabled, want to try and repair what I can. Do not hear any vacuum leaks and checked connections. Considering new plugs, air filters first as I have those on hand. If it makes any difference, car has a worn trans shift lever assembly and bad A/C-heater fan but I do have the OEM replacements. I would appreciate any potential diagnoses and repair suggestions.