Where is the Ecu location in 1991nissan maxima

Drivers side fender well under hood, sometimes behind glove box on passenger side, Maxima used those two locations

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Would it b cheaper to buy second hand ecu , the immobiliser antenna around ignition ignition barrel and key all off same car

This is a copy/paste from a Nissan forum:

C/P

The ECU is located on the floor directly behind the radio. You do NOT need to remove any glove box, dash, or vents to access it. There is a black plastic cover with 2 round plastic snaps that cover the ECU. From the driver's side, the cover is directly beside the gas pedal. Pull on the cover to remove it, and there is the ECU. The ECU has (4) 8mm screws that hold it to the mounting bracket. Then it slides out towards the passenger's side.

As for the part number, you need the Consult-II to get it. But you also need a code that is written on top of the ECU if you are looking for a junkyard spare. You can see this code from the passenger's side without removing the ECU from the mounting bracket (You will need a flashlight). The number should be A56-***-** or something like that.

Relay is under the hood. Dash light could of burnt out. Check out Maxima.org

1998 Nissan Maxima bluebird?
did not bluebird end in 1994?
ill answers for 1998 USA, if car is a JDM , well that be different

you have idle surge, (aka hunt)
the ECU controls idle at all times.
there are 10 or 2o things that can cause surge.
many tests. are you up for tests and buying tools, or just want a wild guess>?
1: EGR mains stuck open.
2: ISC stick (electric idle valve)
3: TPS switch ,not closed, at idle (that kills idle controls dead
4: lean AFR. and ISC has lost control or makes it hunt.
5: intake air leaks.
6: ECU in limphome. the USA cars (no location stated, bad)
all usa cars have OBD2 this year, ever use a $7 scan tool yet?
CEL stuck on running. never pulled the DTC errors?

ill stop here, there are 10 more. at least.

The ecu is located. Behind the glove box. You will have to remove the glove in order to access it.

Rear 02 is catalytic convertor here the thing 5 spped and automatic will not make a difference on the engine management it doenst manage transmission control it seperate in the ECM if you have the old one the prom is removable is you dont lets deal with what you got the rear or is a heated circuit so you need to check for 12 volts on the white wire and ground at the black if it all check out then you need to check the signal wire for activity if you get a lot of activivy you got a bad catalytic

check the fuel pressure to injectors to see if pump is working properly. there should be a schraider valve on engine fuel line under hood to test this. the ecu is located on floor directly behind radio. there is a black cover with 2 round plastic snaps that cover ecu. from drivers side, ecu is beside gas pedal. pull on the ecu cover to remove it. are all fuses and fuel pump relay ok !!

There are only two places it could be:
Attached to the firewall on driver's side of the car.
Under the seat.

i just bought a Brand New EGRC Solenoid control valve but the code still there can anyone help , thank you so much.