Engine misfire with check engine light staying on?

The engine light tells me Code 14 Idle air control valve or bad ECM.
I was right.
I didn't want to use the code reader because I want to learn from sounds and understanding how the machine works.

When it's cold outside, when the wind temperature is below 15 degrees F, then the engine runs just fine until the electrical system gets a full connection from the car warming up and then the engine misfires.
Sometimes that would take up to 3 minutes until the engine starts to misfire.
If it's above freezing, then the engine misfires right away after starting the car.
When the engine started misfiring is when I was driving in a neighborhood.

After I changed the air filter, oil, and transmission fluids. The car seemed to be running just fine in idle until I put the car in drive and then I start losing power when I try to maintain a speed. When I am accelerating then the car runs normally.

After I changed the fuel filter is when the engine started misfiring when I turned the car on. The car still runs normally when I am accelerating but I lose power when trying to maintain any speed. That is when the RPM drops to 1500 and stays there until I start pressing harder on the gas pedal.

Why?
Does that sound like a ECM problem instead?
I don't have a voltmeter right now.

I changed the Idle air control valve because it was very dirty, and the car started up and ran but it was leaking antifreeze.
The hose to the IAC wasn't sealed properly by the clamp so I took the manifold apart and fixed the clamp.
Started the car and it ran but had a high RPM of 2.5 and still leaked antifreeze.
This time the antifreeze was leaking from the gasket on the IAC. I took the manifold off again and I took off the IAC to switch the gasket from the old IAC with the new IAC since the old gasket wasn't leaking and still looks and feels good. This time I added a little antifreeze to the gasket in hopes that it would stop the leak.
At the same time, I unhooked the hose from the radiator to the IAC and drained all the antifreeze and to make it easier to attach to hose to the IAC without so much space restriction.
I reconnected the hose to the radiator and refilled it.
Now the car won't even start. It will crank but won't start. The engine light won't even turn on when I put the key in the ignition to prime the settings without starting the car. Even when trying to start the car there is no engine light turning on.
The battery is okay, the crank is okay.
I'm assuming that the IAC is bad but I don't understand why it would start up before with misfiring, but it won't start up now after I drained and refilled the antifreeze.
Should I pour antifreeze down the hose from the IAC?
I'm assuming that the antifreeze isn't able to push itself back into the IAC.

No, it won't start if I press the throttle as I turn the key. I tried 4 times.
I even tried resetting the IAC with the trick of turning the car to the on position for a few seconds, off for 10 seconds and then turning the car on but it wouldn't turn on.

The space where the IAC is was slightly dirty but I tried wiping the dirt off with a paper towel but it wouldn't come off so I tried cleaning it with a scratch pad and a little antifreeze and wiping it down with a paper towel but the little amount of dirt wouldn't come off so I left it alone since it was running with the dirt on it.
The dirt is stained into the metal and won't come off.
The only other thing I did was, use a paper towel and wiped off the intake manifold temperature sensor since it was dirty on the inside.
The intake manifold is slightly dirty but that didn't stop it from running before. Plus, when I wiped off the temperature sensor, I also tried wiping down the inside of the manifold and most of the dirt is stained into the metal.

When I refilled the antifreeze, I used concentrated antifreeze. I know that I will have to drain the antifreeze again and mix it with water for a 50/50 ratio, but I didn't think that would cause the car to not start.
I'll take it apart again and take some pictures.

Solved the issue.
When I put in concentrated antifreeze, for some reason it didn't go up the hose to the IAC.
I drained the antifreeze and flushed out the radiator.
Then I mixed half and half water and antifreeze in a bottle and poured it in the radiator while the manifold was still off. The antifreeze started pouring out of the hoses to the manifold.
I put everything back together and the car still wouldn't start.
I took the manifold off again and inspected the IAC valve and found a hairline crack in it.
That explained why the car wouldn't start.
I decided to take the old idle air control valve and clean the dirty screen with a paper towel and put it on the manifold.
The car started up and after a few minutes, it started misfiring again.
I turned the car off and waited a minute, then turned the car back on and it ran for 20 minutes with no misfire.
Drove the car a few miles and no more problems.
Well except for the oil light flashing. There is no leakage and the oil light was flashing before the IAC started creating a problem.
There is no leakage and I believe the oil sensor needs to be replaced because I had 10W 30 oil in the engine before and when I changed it to 5w 20 like it should be then the oil light starts flashing when the engine gets warmed up.
Thanks for the help. Much appreciated.

New problem.
My car misfires and loses power when trying to maintain speed.
When I start up the car, it misfires a few times and then calms down to normal.
As I accelerate it acts normal but when I try to maintain a speed then it misfires.
I tried getting a code, but nothing shows up and the engine light doesn't turn on until the engine continues to misfire while driving.
The battery, alternator and belts were checked out. Everything seems okay.
After I cleaned the IAC valve and put it back on, everything was running normal until I turned the heater on and then the engine started to misfire.
Now it continues to misfire when maintaining speed while driving.
I wonder if the IAC is actually going bad.