First time posting as I’m pretty stumped.

I’ve also looked at every other thread on here and haven’t found a straight up answer. Always comes down to the IACV. every other piece I could replace is new.

No vacuum leaks. Timing set right on the dot.

Run down is a 89 240sx hatch. Ka24e. 5 speed. 108k miles. Full timing chain rebuild (100% correct timing as I’ve doubled checked mating marks) new plugs and wires. New coolant temp sensor. New TPS sensor. New MAF sensor. New oil pump/new distributor correctly positioned at 15 degrees at top dead center when setting the timing. I set the timing and idle set screw with TPS DISCONNECTED and it will hold idle at 700-900. Shut off car. Reconnect TPS and it won’t hold an idle. Boggs down and dies. Once engine is above 1500 rpm it runs smooth. Only thing I haven’t replaced is the IDLE AIR CONTROL VALVE. I’m sure that’s my issue but for the life of me CANNOT find one. Any one know where I can find one or what I can do next.

On models that old sometimes the TPS must be carefully set, not doing so might well do that. The beginning voltage of TPS is a pure idle only setting and they signal for more fuel at higher volts, if you are in the higher volts ramp at idle of course it will bog down, too rich.

If you are setting the idle screw too high to artificially jack up the speed like on old cars then it is likely not the IAC, that is all the IAC does itself. You basically replaced it doing that. Look close at what happened when the TPS got plugged back in............

Many change IACs for no reason, it's the super trick buzzword part to change at a bad idle just like everybody changing ATX solenoids on automatic transmissions now for shifting issues and often to no good result at all. Nobody ever thinks outside the envelope and the parts sellers love it. I should know, I used to be one of them. I pushed IACs all day long and often they did nothing.