OK, I will NOT replace any EGR components for the time being.

As for the Coolant Temperature Sensor, could this part needing to be replaced somehow have been causing the misfires in 4 of my engine's cylinders? Perhaps, because it was not functioning properly and was causing my engine to run at a higher temperature than it should be running at?

If the Coolant Temperature Sensor could not be the cause of the misfires, what is a likely cause? I already got new spark plugs a few months ago, thinking that was likely the cause, but the error codes still showed up after having Auto Zone check again, and the misfire/stuttering/hesitations have still been occurring.

Also, could the Coolant Temperature Sensor needing to be replaced possibly cause the engine to run hotter and/or somehow have contributed to the overheating issues?

I realize that I apparently have a cooling system leak somewhere, but, something likely caused the leak to occur, right? Like, my extremely fast/hard driving after leaving late to work and putting major demand/pressure on the engine? And/or the Coolant Temperature Sensor not communicating the engine's temperature properly and, therefore, not allowing the cooling system to work properly/effectively? Or am I wrong about this speculation?

 

By the way, if you happen go read this post shortly after I post it, I wanted to ask a couple things about the actual process of changing out the Coolant Temperature Sensor, before I actually attempt to replace it.

1.) Do I need to disconnect the battery before doing the removal?
2.) Should I take off the radiator cap and make sure that there's no pressure in the system?
3.) Are there any other specific things that I might need to do before starting the Sensor removal process?
4.) Is letting my car sit for an hour after last driving it likely long enough for the engine to cool down enough to do this task?

 

Al the coolant temperature sensor does is measure the coolant temperature. The sensor will not cause the engine to run hot.

The coolant temperature sensors sends the temperature to the engine computer. The engine computer will start adjusting the amount of fuel to the cylinders when the engine reaches a certain temperature. If the engine computer can not see the engine temperature, I think it will add too much fuel and can cause a misfire. That is why I suggested to fix it first.

Removing the radiator cap and disconnecting the battery are good precautionary measures, but not the end of the world if you did not do this.

Dont worry about the maintenance required light as it turns on after a set number of miles to remind you to get your car serviced. You should make sure it is reset when you do your next oil change.

The overheating is the next issue you need to address. Overheating from coolant loss is due to some type of leak. The leak can be a cracked hose/radiator or possibly a blown head gasket. Pressure testing the radiator can help find external leaks. Hopefully your issue is a worn cooling system component and not a blown head gasket.

That is another reason why I keep telling you to hold of on the EGR system, because you have more important issues to address first. I do not believe your EGR system is having problems. The minimal work I would do is clean the port, but you have bigger issues to address first.

 

Do you see any wet spots on the ground where you normally park? Just asking as this might give you an idea of where an external leak might be coming from.