What does the engine idle at with IACV disconnected?
What are the compressions like ? Are they more or less even across all cylinders ? Also was anything done that could of affected the combustion camber volume in any of the cylinders (this can include valve lapping) ?
Might sound stupid, but have you tried bleeding the coolant again?
Do it with the front end jacked up and run the car with the heaters full hot until the fan comes on a few times, front end jacked up with the cap off helps the air out as puts the top of the radiator at the highest point
With the huge koyo radiator on mine i always have to bleed it a couple times to get all the air out, usually doesn't cause much of an idle issue but will cause the revs to drop more than they normally do when coming to a stop if there is still air
Hopefully your tuner can smooth it out for you then or point out what it could be. I hate little things like this.
When warm or cold?
Warm....Disconnect IACV plug when running and see what it idles at
Might sound stupid, but have you tried bleeding the coolant again?
Do it with the front end jacked up and run the car with the heaters full hot until the fan comes on a few times, front end jacked up with the cap off helps the air out as puts the top of the radiator at the highest point
With the huge koyo radiator on mine i always have to bleed it a couple times to get all the air out, usually doesn't cause much of an idle issue but will cause the revs to drop more than they normally do when coming to a stop if there is still air
Here's normal idle when warm (Fan not on)
Here's normal idle when warm with IACV unplugged (Fan not on)