Update 2:
New ECU has seemed to do the trick as I havent stalled again since installing it over 300km/ 1 Week ago (it was stalling pretty frequently beforehand like every 10 - 20km). Thanks for the help everyone.

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Update: 
So I replaced the O2 sensor & my idle revving has sorted itself. Now I am trying to sort the stalling. Yesterday I it went to stall again (lost all engine power but instruments stayed on) I was slowing down from 60km p/h. Got to about 35km p/h and then it found ignition again (sounded like I keybanged it haha) & off she went. Electrical problems are so frustrating. I will be pulling out the ECU to look for any glaring issues this weekend.
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Hey Forum,

So my newly rebuilt MR2 has got a bit of a weird problem. I just wanted to get some idea's on what could be causing this problem. It's a 1992 SW20 3SGTE
 
Symptoms:
- Bouncing Idle - Between 1400 - 600 rpm.
- Intermittently stalls, pretty much it doesn't matter what I'm doing, what RPM or speed. My instrument cluster stays on but just stalls out. It wont kick over again straight away. I generally wait for about 5 minutes & it'll kick over again.
 
Now yesterday I decided to take a decent run to see what would happen. Drove 10km and it stalled at 100km/h. Waited approx 5 minutes and it kicked again. Then drove another 75km at all different speeds, the car made boost fine and drove really well, before it finally stalled again at approx 40km/h. After this stall - I couldn't get it to kick again. Tried for about 1 1/2 hrs giving it 5, 10 & 20 minutes break in between attempts. (Luckily I was close to a pub with beers, pokies & a good Chinese restaurant  ). So I towed it back to work where again it wouldn't kick when I got back (About a 30minutes trip). Come into work this morning it kicked over with no trouble 

Before I bought this thing it had been stored in an opened wall carport with just a roof overhead for about 3 - 4 years & was in pieces. 
 
My Thoughts:
So personally I'm not a mechanic but I seem to get power everywhere I need to. My O2 sensor is super dodgy, I dont know if it could cause this problem but it is a 1 wire O2 sensor but it was cut along the loom, so I dont know if it was originally 2 wire and was converted to a 1 wire. The rest of the things like Dizzy & AFM were cleaned up & reused - it could be one of those things. Just like to know what you guys think. 
 
Thanks
Jarrad

Fuel pressure... have you checked or replaced the fuel pump?
 
a bouncing Idle can also be a sympton of air in the cooling system

@carmikey I got a 2nd hand tank as the one I had was completely rusted. Not sure if it was an NA or Turbo tank. Fuel Pump seemed to work when I put power to it. If it was a NA fuel tank, would this be an issue in a Turbo car?

Hyldnir
@carmikey I got a 2nd hand tank as the one I had was completely rusted. Not sure if it was an NA or Turbo tank. Fuel Pump seemed to work when I put power to it. If it was a NA fuel tank, would this be an issue in a Turbo car?

I wouldnt think so, not unless you have a heavily modified engine with lots of boost. From memory, the stock NA fuel pump is good for upto & around the 200KWs at the wheels. Someone else here would know better I'm sure.
 
I have had simular experience as you have mentioned, turned out to be fuel pump, although one day it would run just fine, other days no so... fuel pump in the end

I have thought of the fuel pump. It's weird I can make boost and drive for long periods without it failing tho and then boom it fails ... this is going to be one of those tricky ones I assume :) Replace parts & parts til its right. Mechanics at work seem to think dizzy ... 

Hyldnir
I have thought of the fuel pump. It's weird I can make boost and drive for long periods without it failing tho and then boom it fails ... this is going to be one of those tricky ones I assume :) Replace parts & parts til its right. Mechanics at work seem to think dizzy ... 

There is a little wire at the back of the dizzy that is often very brittle, double check all those things too. Hope you find the culprit, please keep us updated on your findings

Just pulled my O2 sensor off, i knew it was pretty bad, but damn. Part no# is an australian celica 3sgte one. Not the factory MR2 one. Dont know if thisll make a difference tbh

The diode on your ecu can be on the way out as it heats up with use it fails is now 27 years old swap your ecu or swap with an another to check. This has happen to me.

grosso
The diode on your ecu can be on the way out as it heats up with use it fails is now 27 years old swap your ecu or swap with an another to check. This has happen to me.

Once I open the ECU, is there any other way to test the ECU other than just visually checking all the diodes & capacitors?

I unfortunately dont just have another ECU lying around.

Jarrad

Firstly look for any swelling or leaking capacitors. That's normally the first indicator of them failing or on there way out. As for testing, I'm sure it could be but probably easier to swap over with someone's that's working fine.

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