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Hello, thanks for posting
Do you have the code numbers at this time or can you post them here for me, an IAT sensor malfunction should not cause a misfire.
Is it a 4 cylinder or v6 engine?
Have you checked the engine compression yet? Have you checked basic things like spark plugs, plug wires and the connectors. I think your getting this code due to another problem with the engine, try to find the reason for the misfire first.
The ecm itself can't be checked, at least not even at the dealer level, there are some facilities that claim they have the test equipment to test them, check online. The only other thing you can do is to use a manual and check the wiring between the sensors and the ecm, it could also be a bad ground point for the ecm, you might want to go there first, check all computer ground points and check the ecm connectors for corrosion and bad connections, to check grounds it's best to disconnect the battery to take all power off, then check the brown/black wires from the ecm these are grounds, also check ground connections on the engine intake manifold area, computer grounds must have less than one ohm resistance to body ground.
Less than one ohm is good/
I would check around for a used ecm, making sure it has the same part number and give that a try, or buy an exchange unit, there are places online that remanufacture them.