2001 Maxima idle erratic

[Dansmaxima]

I got this car with 94k. California car. SEC light has always come on intermittently. Every 200miles or so. I think the code was 0420-catalyst. Now it is idling erraticly 1500-1800 rpm way off. I replaced all O2 sensors with universals. Does it matter where the white wires connect to the original harness? In other words the white wires are indistinguishable. I checked the iacv-aac valve and the ohms were out of specs. I just put in a junkyard one, still the same problem. If the idle is cycling erraticly, the iacv-aac valve must be working? Tried to reset idle learning by briefly disconnecting tps brown connector as described. Cleared codes with a gst. Junkyard guy thinks it's a vac leak. Could it be the mass air flow sensor? I'm stabbing in the dark here. I have the factory manual. I was advised against universal oxygen sensors. I really need further assistance!! Thanks, Dan