83 280zx non turbo 5 speed runs rich. heavy black smoke/ soot coming from exhaust. rough idle before warm up. how do i fix this problem?

Need a little more information...mainly, when did this start? Did it start after you put on the Cold Air Intake? If yes, check any related sensors first for condition and proper connection... MAF and IAT..... very important to mixture control. If there's no connection with the Cold Air Intake, there's a few possibilities and it would take some diag work to narrow it down.... Stuck EGR valve is one possibility. Another possibility is if the fuel pressure regulator operates on vacuum with a diaphragm, sometimes the diaphragm will blow which will increase the fuel pressure and also allow fuel to be sucked through the vacuum line directly into the intake. I'm not familiar with the fuel delivery system on the old Nissans......I'm assuming it's an early generation fuel injection setup though...?

on these late models check all your vacuum lines they are notorius for hardening around the nipple hook ups and cracking there i had the same problem on my 83 turbo if left to long it can cause damage to the engine one trick is get some rubbing alcohol and start car pour some of it in a small cup 4oz. about disconnect a vacuum line to the intake manifold leaving it connected to the manifold allow the hose to slowly suck it in with out stalling the engine and plug it with your thumb this will clean you maybe running to cold of spark plugs