You'll need a multimeter to test your IAV. Despite it being clean.
You'll need a wiring diagram for it to and find the signal to ecu wire. Test it for voltage (20v max) and resistance.
I had a car in not long that ran alright most of the time then lumpy and would overrun. Despite what you might expect... it was the water temp sensor
Have you checked cambelt/chain condition? Or the O2 sensors?
Does yours have a cam angle sensor?
Its a tedious task but its worth checking all your sensors. You'll only get an ecu fault if the sensor fails, not if it's giving a signal despite how poor. Like migs said its worth checking all your values fed into the ecu. Quicker than a 1 by 1 test
