Engine stalling, looses power, then hard to start

Seems the idling speed is too low and I would suggest cleaning the throttle body and IAC and retest. Dirty throttle body and IAC would result in low idling and stalling after warming up.

We won't rule out anything for now. The normal procedure is to start with the basics and cleaning is not going to cost you much. Replacing components could be costly and might not resolve the problem if it is not the cause.

Cleaning the throttle body and IAC only helps and causes no harm. There are aerosol carb cleaners available at parts stores and the best way is to remove the throttle body and separate the IAC from it for cleaning. However if you remove the air hose and use a tooth brush and rag to clean the throttle bore, it works though the IAC cleaning might not be thorough. Point the nozzle into the port at bottom of throttle body to clean the IAC and let it soak for a few minutes. Repeat the process a few times and allow the carb cleaner to evaporate before attempting to start as excessive carb cleaner would result in flooding and difficult starting.

Initially the engine might be difficult to start and satll upon starting but that is to be expected, until the carb cleaner clears off.

The idling speed should increase and it might take some time to settle back. If necessary, repeat the IAC cleaning after running the engine for a few minutes.

If trouble codes had been recorded, they would be in memory until they are cleared.

Were the spark plugs checked/replaced?

Try driving around for a while and see if there are any improvement. /You might need to repeat the cleaning process again if the result is not satisfactory.

I never have a good relationship with additives and don't think they are much of a help, at least that is what I have experienced. You could have bad fuel in the tank and draining and refilling might help.

As problem seems to be temperature related, the next thing on the list to check would be the Engine Coolant Temperature sensor. Most sensors would throw error codes and the MIL not indicating does not necessarily mean there are no codes. Some codes requires a 2 trip detection and some don't trigger the M IL.

Check for trouble codes and if possible, monitor the ECT operations.

Yes, you should be checking the fuel pressure. I missed out the date you replaced the fuel pump and thought it was recent. Fuel pump can go bad but sometimes it is just the hose connecting the fuel pump to the housing that is leaking resulting in pressure losses and difficult starting. This would also reduce engine performance.

The best way to test the TPS and IAC is to use a scan tool to monitor their range while in operations.

You cannot clean the TPS as it is a sealed unit and is a variable device for different resistance at different throttle opening.

As to IAC, you need not adjust it as the engine computer would automatically reset it depending on signals from other sensors.

If you test the fuel pump pressure and regulator, you would be able to find out if they are faulty.

I wonder why your manual mentions testing relays coils for resistance. What you should be testing is if the relay is working and the resistance should be for the main power supply through it.

Sorry for the delay in replying. I was away for the past few weeks.

*How much should the end piece (Pintle) go in and out? When I had my wife start the Tracker, I watched the Pintle move a little at the end, but not a huge movement-

Movement of pintle depends on how much it was out previously and engine temperature. It usually moves only slightly.

*When I have the IAC Valve removed, how far inside should I spray cleaner into the small hole? Should I use specail cleaner or just carb cleaner for that area?

Carb cleaner should do.

2) After spraying throttle body cleaner inside the intake throttle area, I left the car for a while for the spray to work. Once I came back I tried starting the car and it would not start at all! When I clicked on the ignition it would not turn on. After waiting a bit longer I was finally able to try and start it, but it would not start as it sounded flooded possibly all the spray I put in?

Yes, after using carb cleaner it would usually require some cranking before it fires up due to flooding.

I ended up having to charge the battery before I could get it started 60 minutes later. Is this normall? The battery is about 3 years old but checks out ok.

Cranking time depends on battery condition/charge and amount of cranking time and if you are able to fully charge it without any starting problem, it should be normal.

*With the engine running I unplugged the IAC Valve harness.I did not notice much of a difference with it plugged in or not plugged in- Could the IAC be the problem?

Since pintle was moving in and out when you tested it, it should be good. Disconnectting the IAC would not make much difference in idling speed as the pintle type would remain where it was at the moment it was disconnected. If you disconnect the wire when engine is cold, rpm would be higher then idling speed.

Is there a better way to check the IAC Valve? What exactly should that end of it be doing? How far in/Out? Movement, ETC.

A scan tool would allow you to actuate the IAC movement

4) Also with engine running I unplugged the air filter housing and took the air cleaner out, then engine remained running? Is that normal or should it have stalled out?

Removing the air cleaner does not affect the engine operations unless the MAF was disconnected.

ONE OTHER SIDE QUESTION:

5) When a fuel pump is changed, should the mechanic replace the little rubber gasket that holds the fuel assembly to the actual tank? The times I have had the pump replaced, the mechanic just -reused that gasket! Could that be part of the problem?

The gasket is only for sealing purposes and if it is not leaking, it should be good.