86 300zx stalls when warm

86 nonturbo 300zx a/t w/202K miles on it stalls when warmed up. Driveability is jerky at best. Replaced cap and rotor w/Nissan one, tried gumout intank, disconnected fuel temp sensor w/no change, changed 02 sensor,spark plugs(oem)chaged 20K ago, plug wires 30K old,tried different octane. Funny thing though I can drive 50 miles on the highway at highway speed with no problem but once I get to the off ramp at a stop light the problem comes. ECU codes are 12-(low out volt when eng is low),21-(ign sig not entered in 10 times),31-(on/off sig not entered when ign sw not turned on),41-(fuel temp sensor opened or shorted). Funny thing though I had these same codes back in 2001 when I ran an ECU test for another problem so I do not have much faith in those. All help appreciated. Grey-hound