the factory NGK Platinums. What was the plug # on the Iridium you used? Most plugs do not have the right nose length and therefore it doesn't sit in the combustion chamber properly, nor always the right heat range. On the other issue, I say pull all the connectors with the spring clip and clean the terminals. They have to be 100% clean and make good contact for the engine to run properly, especially the Coolant Temp Sensor, CAS, PTU, MAF and AAC.