E30 Zone

My 325 has developed (rather suddenly) a fairly constant misfire on one cylinder (no 2).
I've changed the sparkplug, HT leads, injectors and blue temp sensor, none of which has made any difference.
The end of the plug is coming out black, but doesn't appear to be oily. I can swap it with another plug in a different cylinder, but it's still the No2 that doesn't fire, the one that now has the black plug runs fine.
The injectors are all ticking away all the same.
I get a nice fat consistent spark from a plug in the No2 lead sat on the rocker cover.
I've also checked the compression in cylinders 1 and 2 (too cold to do the rest!) and get 150psi (cold) in both.
It will sometimes clear as the engine is warming up with the gauge passing through the blue, but then the misfire comes back and stays.
I can also sometimes get it to clear by running up to 3k rpm in second then lifting off (so the injectors shut off), I can then put the throttle down and it'll pull cleanly - until I change gear or slow down etc.

I'm a bit stumped now. Any ideas?

Have you checked the engine loom plug under the inlet manifold? ..

Thaks willnz, I'll give that a try in the morning. I've had a look under the rocker cover and all looks fine in there. Injectors have all been changed for another set I had.

Right, just tried that. Get consistent 12v on all 6 connectors. Also tried a loop of extra wiring between 2 and 6, but this made absolutely no difference.