Have you checked your fuel pressure. For the most part rough idle is a vacuum leak. have you inspected your EGR tube. You can't test this by spraying carb cleaner on it. You actually have to take it off and hold it up to light. The only sensors that can cause rough idle is the IAC, make sure it'* all clean, if not that cone won't seal up. The MAF sensor can cause problems if it'* dirty.

Will have another look, I just have to walk away from all this for a while, I'm getting too frustrated for now...mebbe have a beer, come back later

Thanks for the input, I'll post again later after I've had a chance to revisit these possibilities.

Sometimes that'* what you need to do. Plenty of times I've been scratching my head, then finally walk away. I'll be sitting there when it comes to me. You will get it, and then smack yourself, dang, why didn't I think of that right away. When you shut the engine off, listen real close, do you hear any hissing?

I would OHM out the coils, not just to make sure they are within spec, but also the closer they are to each other, the better. The other thing I would ask about? How clean is the engine? I would run a seafoam treatment, blast the crap out of it, then change the plugs again.

its either a custom or a limited, it cant be both :/

I had this problem once, one day I started my car and it sounded like a derby car had no idea what was going on, took it to a gm dealership they ran it for a little while and suddenly it was fine again. Apparently there was a chunk of engine sludge in a line somewhere causing it to cough. Try running it for a while, do the sea foam deal, and start using gumout when you do oil changes. I started that routine (minus sea foam) and my 96 lesabre custom runs like a champ.