Will toyota corolla 1800 with 1zz motor run with 1600 3zz ecu.

2003 up corolla models may have one air bag
if so the air bag is part of the horn pad

air bag light and chime would be there only
if air bag system is faulty

You cant. It controls everything required for the engine to run. Timing, fuel, air etc.

Ign is for ign , stop is for brake lights, s heater is for blower motor, ecu is for computer, ecu ign is for distributor, are you looking for a specific problem

pls check whether the Radiator fan is running when the ignition is switched on. If so, it means the Engine coolant temperature sensor is out. Replace this. Then the AC will work. This is one of the reason.
Check the thermister, pressure switch, wiring harnes and the ecu. the relay etc.,

Change the ECU to the 1800

run fault codes and fix faulty sensors.

check the idle solenoid on the carby is connected or the idle sensor is ok

first, there is an open recall for ecu problems on corolla, have your vin run by your toyota dealer to verify, hope you still have your old ecu,a new is around 1,800$ plus reprogram and re-write the vin on new computer, dont know if they will program yours(used) ask if there no other option.

if it's only a leaf perhaps you could blast it through with an airline. the type used to inflate tyres.