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Alfa idle blip

I have a 1990 Alfa spider. It has a blip at idle. Originally it was much worse. Idle would drop to 500 then pop up to 1200 the back down, back up etc. Engine would sometimes stall while driving. This happened as I would take my foot off the gas coming to a stop. I replaced the first large air duct between the mass air flow gauge and the air intake chamber(cracked on underside). Helped some, but still had blip which was then unpredictable. I cleaned the air flow gauge and the constant idle actuator with air flow cleaner. This helped more but I still have the blip during engine warmup. Idles fine at start up, blips for a while, then stops bliping as engine nears running temperature. What should I do next?

I’d look at every possible source of a vacuum leak, cracked/loose hoses, fittings, gaskets, etc.