1989 240sx KA24E Stock. Recent idle/missfire problem.

[xs04298]

Thanks in advance for any possible leads.

The car has quite suddenly (progressivly over say a week) developed a misfire at idle, a fairly preditcable pattern.

Morning after sitting all night, starts, idles at 800rpm as ussually but rougher than it used to be. stays at that condition for the next 2 hours to destination. sits for 3 or 4 hours, then i go to start it again and it'll start right up, go back to idle of 800 for about 5 seconds, then it will drop to 400-500 (the drop has gotten worse and worse with time, nearly stalled today) and will stay at that level for about 20 minutes, then it will go back to normal speed but still rough. It is very rough when the idle is low and i can feel see and hear it misfiring.

Things i have checked:

All vacumm lines, attatched/electrical connections pluged.

All sensor connections, including swaping the tps (had an extra just trying to figure it out)

pulled all the plugs, very even, not flooded, maybe a hair lean? all plugs sparking (at least as well as i could tell normaly)

ran it down on gas and filled up at a good station (in case of bad gas)

checked the negative cable resistance and ground resistance (back of engine)

nothing has changed though, just keeps getting progressivly worse. I know IACV's get dirty on KAE's but it seems hard for me to believe it would be clean for a year then within a week span become dirty, but you never know...ive unpluged it at idle and there is absolutly no change in idle, still missing just the same, not sure what that means if anything lol.

Sorry for the long post just trying to be as detailed as possible,

Thanks again for any advice