Missing at idle and low load, hmmm.
What computer are you using?
Last time I saw this it was bent valves, sorry.
Could also be vacuum leak ie. those mystery hoses, that is throuwing out the mixture.
Ignition timing? 12degrees BTDC for the 18RGEU.
Could also be cam timing. It f it is at TDC for no.1 and you put the top off it, there are two little timing marks just near the timing coggs. They look like square notches out of the circular thrust flange. These should be in the 12:00 position, vertical, both of them.
I'll see if I can put in a picture, as I can't remember much from last time I saw one in a car.
Now to try for the picture, I hope it both helps and works.