help needed if possible?

When i was running standard about 5 months ago it'd idle where the revs would go from 900rpm to 1000rpm Then it stopped doing it. Its just returned again.
I took out the icv and cleaned it and its not improved this problem.
It idles up and down from cold and hot,, and theres a very slight jump misfire every now and then below 1000rpm but not in rev range above..
It drives absolutely fine,, boosts fine etc,, but idle is allover the place.
I'VE JUST fitted a msd stage 3 chip its been fine for the week i've fitted it unitl now?

Is it CO2?
Idle base out?
new Idle control valve?
fUEL pRESSURE.