I need to remove and replace my ECU. on 1995 Nissan Quest

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I have located it (or them) behind the glove compartment. There appears to be two units mounted one above the other. One is larger than the other. Which one actually controls engine function and how is it removed?
(3) Answers
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Before removing the ECU its best to test each wire at the computer looking at a pin out chart to see if the signal is supposed to be power, ground, pulsed sine wave or hall effect signal, you look for voltage drop on the signals or no signal at all. Roy is right check the MIL light bulb first the ECU grounds the bulb to light it. Your car has a OBD2 diagnostics so a good scan tool should test a lot without having to intrusively test each sensor value. If it is the computer a company called Fuel Injection Corporation in Livermore California can test the computer for you they are very good.
then you may want to go to a shop that can accurately check the failure and give you a bid.

By paying for a proper diagnostics may save you much more, then replacing parts that you dont need. You might need a $30 Throttle Position Sensor or a crank sensor.But without diagnosis its all just guess.Expensive guess.
why are doing this repair?? it is the last thing you would do when doing a diag. very expensive guess.

Van starts and idles normally, however engine is "hunting" at 2200 RPM. At 2200 RPM the RPM's fall and range between 1500-2200 RPM when pressing down on the accelerator. I changed the gas filter,checked and cleaned the IAC valve. Check engine light does not come on at any time even when ignition key is turned on so I believe it to be faulty. Fuel pump is putting out normal pressure. Can find no other obviously problems.
i would have the computer scanned first. it may be a burned out bulb.

as far as the hesitation, did you check the fuel pressure with a gauge??

Well if it's not the ECU what do you think is the problem? It's not the fuel pump as it was checked for pressure output and had textbook pressure. Keep in mind that it starts good and holds a steady idle at 900 RPM's.
The larger unit is the ECU and the smaller is the TCU(Transmision Control Unit) You have to use 10mm socket to remove them(same bolts holds both unit together). First remove negative battery cable to avoid damage in units.
Are you referring to the single 10mm bolt that only seems to hold the plug in wiring assembly on? Can a ECU be bench tested once it is removed?