Z31kingboi

Hey all new to the forums and z-life here. I purchased and N/A z31 recently. Flushed and swapped all fluids, cover gasket heads, valves, hoses, and spark plugs. The problem I am having now is with the idle. Back when I first bought the car I noticed it would idle a bit rough. Today, however, when I turned the car over it would sit at 900rpms for about two seconds, then incrementally drop to 400 before dying on me. I found that for short term I could just give it a bit of gas to keep it from dying but the problem is still there. I am farely new to this car so any help, advice, or diagnostic given would be very helpful.