What it is:

86 Pontiac Trans Am
305 SBC with Holley Stealth Ram TPI
Stock or no bigger than stage 2 cam.
New Plugs
Newish leads
Newish Coil
Newish Distributor (External coil - not in cap)

What it's doing:

At Idle, there is a faint miss, almost like it's intermittently running on 7 cylinders. When it's cold it's not as bad, it gets stronger as you get to normal operating temp. The miss is sort of like a pum pum sound every so often. Then if you hold it in first and rev it high around 4000 - 4500 it's really missing and breaking up and sort like surging, even small back firing. But normal cursing it's totally fine, you could not fault it at all. It did have a slight surge at 2000rpm but that's even gone once the 2 injectors were changed. The problem is just idle and high revs.

I have checked all Injectors for 16 ohms, and replaced 2 suspect injectors.
New plugs - also have re-done gap size again. Now opened up to 40thou.'

With out going the next stage and spending heaps of Money: Changing Cap, Rotor, Plugs (again), Leads, Coil and a new set of 8 injectors all at once. I'm really unsure what it could be. I have a new sensor kit coming, but I don't think it could be this as it's there when cold and hot, but like I said gets worse when hot.

Any ideas?

 

well you could take a test light while car is running and probe the plug wires at the cap to see if you can narrow down what cylinder is not getting proper spark ,if equiped check EGR valve

 

might try opening the hood while running in a very dark area, (don't get caught in the parts), and looking for a spark jumping to the engine from the plug or coil wires, or across the coil or something.
its free, and worth a try.
sometimes the simple things might save you big $$