This problem all started from a clogged cat on highway traffic So far new ICM, cat converter, o2 sensor (downstream) and plugs & wires (rechecked plugs and wires for assurance) and still random sputters. Now code 300 (random misfire) so replaced coil pack and still random sputtering. When sputtering foul smell looked under car and cat converter was glowing. Solve one problem then get another any ideas to fix random misfire?
So far replace: ICM
Plugs & Wires
Catalytic converter
o2 sensor (downstream)
Coil Pack
stuck on trouble shooting code 300 (random misfire) ANY IDEAS?

 

The downstream O2 sensor does not affect how the engine runs, it only monitors how the cat is working. However the clogged cat could have easily damaged the upstream O2 sensors and they may or may not set a code. Random misfire could be due to a ignition part that affects all cylinders, such as the ICM, but you already replaced it, so you may want to check the plugs and make sure they are properly gapped. That being said, the usual cause of random misfire is a lean fuel mixture, so it would be a good idea to check the fuel pressure, and make sure the O2 sensors are switching voltage at a rapid rate. When an engine misfires due to a lean condition the unburnt fuel gets dumped into the exhaust and burned in the cat. This overheats the cat and it soon fails and the O2 sensors follow, and the whole thing repeats.