My ED has began to idle a little bit rough once it has warmed up and the tacho fluctuates slightly so I'm thinking perhaps it may be the idle control solenoid? Any way of checking it to see if it's functioning correctly?

Unplug it and turn the idle up to ~750-800rpm when warm. You'll soon be able to tell if its the ISC.
Or grab one from the wreckers and swap it.

Or you could give it a quick clean out with some carby cleaner. Worked wonders for me . Had some bad starting issues with my Fairmont taking a few attemps to start, cleaned it out and it fires first time now. If that doesnt work you can always try a second hand one from the wreckers as krisisdog said

I got one from the local wreckers today and tried it and it is still the same. But the weird thing is that I tried it with the ICS unplugged and it made no difference to the idle.....Not even the revs on the tacho fluctuated or anything.
So now I'm confused as what to check next.