I have just finished a Gen3 transplant in my car and I need an OEM Gen3 ECU. Before I buy one, does anyone know if the OEM ECUs vary from year to year like the Gen2 ones? If so, how do I identify which one is right for me?

nope, well there are some with traction control. but extremely rare, and still useable.

The Celica ones are different to MR2, but might still be usable

The sw20 gen3 ecu is 89661-17460

celica ones you need to mess around and trick the ecu to think it has the pump and wta intercooler setup. easy done, but then you also loose power steering if your mr2 has it.

so yeh, get an mr2 one.

Great. Thanks for the information.

The celica (St205) ECU does have a 'slightly' better map. You don't lose power steering, but it doesn't have the control on the power steering like the MR2 ECU does.
 
I.e you can enable power steering, but it comes on when you simply have IGN on, even when the engine is off. You can always control manually yourself via a relay to trigger when the engine is running or some other trigger point.

oh, interesting. im sure when I switched a gt4 ecu into my sw20 the ps didnt work. tho that was an earlier rev1/gen2.

so does the ps ecu still control pump speed etc?

Gen3 turbo ecu on ebay now. $110 plus post. I think a member on here is selling it.

Just Ace,
 
The Power Steering ECU has a separate speed sensor pin so the Engine ECU Doesn't control this. All the Engine ECU does is tell the power steering to turn off and on. (There are 2 power steering pins) This is certainly on the later electrical speed sensor cars. Not sure how it works with the mechanical speed sensor ones.
 
When swapping the ECU, simply unplug one of the Power Steering pins (PS or PSCT - can't remember) and the power steering pump will activate when the key is on IGN.
 
I never noticed any issues at Highway speed running it that way.