Could clean out the Idle air control valve (IACV)
Located on the back of the inlet manifold
Make sure the engine is cold. Pull off the 2 coolant lines under it (cloth underneath as a little coolant will spill out), disconnect the plug that goes into the black end of the IACV, undo the 2 12mm head bolts and remove the IACV making sure the small rubber seal doesn't get lost!
you will notice there are 2 holes, one of which has a gause filter, squirt carb cleaner into both until no more dirty fluid is coming out (takes a couple minutes, at first mine looked black inside and then after you could see the white of the plastic bit inside), shake out any fluid then leave to air dry (i left mine overnight)
Reassemble the whole lot, you will need to bleed the coolant system after.....
To bleed the coolant system, remove the radiator cap, run the engine until up to temp (i held the throttle at 1.5k/2k revs to speed this up), you will know when it is up to temp as the lower rad hose will get hot as the thermostat is fully open, put the heaters on full heat and full speed with the setting as straight into your face (makes sure no bubbles stuck in heater matrix), keep the car running for a bit until no more bubbles can be seen in the radiator (if you rev the engine and the coolant level moves up and down there's still air)
turn off engine, top up coolant if needed, should be good!
If the IACV is dirty it can cause fluctuating idle, similarly any air in the cooling system can do similar
EDIT - If it is still doing the same then recheck the valve clearances, when you had them checked was the engine STONE cold? Also was a new valve cover gasket fitted after with honda bond in the corners etc?!
