Car will start and run for about 1 minute then shuts off.Changed the spark plugs and car seems to run better but it still shuts off. after 15-20 mins it will restart and shut off.

I have a 98 explorer and had a similar problem. It wound up being bad spark plug wires. So I changed them and the spark plugs while I was at it. It ran great and still does. I'm not sure if that's your problem I would need more information.

None of those would cause a P-171 or P0174. Vacuum leak is the most likely cause.

Engine stalls or RPM fluctuates at idle up and down.

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve but always run a OBD2 fault code as well as the cleaning procedure. Buy a can of throttle valve cleaner (do not use carburetor spray cleaner!) from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control

This could be several possible causes. If possible I would find out what the spark plugs looked like when they were pulled from the engine. Since you had the radiator changed assuming that diagnosis was correct for the overheating you may or may not have more severe internal problems with the engine. Start with what the spark plugs looked like and possibly what the present spark plugs look like.

replace engine coolant temp sensor

I would start by changing spark plugs, if you haven't changed them in a while. If it has been wet there, raining frequently, then maybe spark plug wires too. That would maybe make sense why once it warms up and drys out it will start ok. I am not sure whether Subaru has the typical fuel pump problem or not, on my vehicle that I once had I turned the key on several times to cycle the fuel pump and my car seemed to start better. If that helps, it is just telled you that you better get the fuel pump replaced. Please rate my answer so I get points for it.

Plug do not come pre gaped. Pull the plug and set the gap.

Did this start when after you changed them?

I would look more to the fuel pump failing than plug wires.

Sounds like you need to Replace the Ignition Module.
It is a square box located on the side of your fender wall when you lift the hood approx 6 by 8 inch flat box shaped.
Go to auto store and they can show you a pic of it.
It Controls Spark plug Firing.
hope that helped