Procedure to re-set ECU on 2011 Nissan Xterra

To reset everything, you can dis-connect the battery.
However, There is an ECU fuse under the hood fuse box. Remove it and wait a minute to reple.

For both number 2 and 3, the is a electroctronic device at the butterf;ly on the throttle body intake. Remove the wire to it and both will be reset. DO NOT attempt to re-postion this part.

The Idle Air Control Valve is in the back of the intake manifold and has coolant lines running to it. It is sometimes hard to get to the electric conncector. Remove it and then reverse procedure with attaching battery last.

1. Leave it disconnected at least a minute.
2. I did mean to use the word replace.
3. Most ECUs will get reset upon battery removal, (Remeber you will need your radio anti-theft code to re-set the radio), but some don't. I cannot make that in %100 because I am not the knower af all, so I like to take it the two ways I know work.
So, when we go through isuues 1-4, this is resetting each sensor with battery attached. It is not a bad idea to go either way with the throttle position snesor and the IACV. You can connect the battery after a minute and then go and dis-connect each sensor to re-set them or leave it to the battery to re-set or do both.
As far as, "starting from scratch". There throttle position sensor is adjustable and is set to an open and closed throttle voltage.
The IACV is not and feeds of engine load. So, some stuff is kinda from scratch and some is hald re-set as it is adjusted to a certain voltage.
I could not find the exact model for your car, but hear is a walk through. Most Hondas and Nissams are set at .5V throttle clossed and 4.5 throttle open.
Follow this link and it will give you a better understanding. But, don't adjsut it unless you have your specific schematics and specs.

https://www.2carpros.com/questions/mercedes-benz-300e-1988-mercedes-benz-300e-throttle-position-sensortps-adjus

5. I have never heard of re-setting in that matter.

6. It is worth trying. If it does not work the fuel pressure should be checked and the TPS and throttle body clened at intake to assure ports are clean.
Try running 2 cans of either SEA FOAM or BG44k Fuel system cleaner. They are the only two that work really well. You might have to go to a service station to get them. You will probably need to replace your oil afterwards as they work so well all the deposits they remove end up making the oil dirty.

Sorry I make so many mistakes typing. We get busy sometimes.
Let me know how things progress.