TwoDogs
... and then the adjustment in the AirFlow meter thingy at the air cleaner. 

 
I had issues with the AFM when I had a ST185 Celica (same engine setup as the MR2 GT)
I did fiddle with the screw in the AFM to make it better, though I was guessing. 
To test to see if it is the cause of the problem, see if you can borrow another one that you know is good to see if the issue goes away.
New ones are ridiculously expensive, so don't even think about that as an option.
As mentioned previously, it is a good idea to get rid of the AFM completely and get a plug-in Link G4+ ECU that is configured to use a MAP sensor to sense load. You can also add a wideband O2 sensor to them and use closed loop fuelling.
You'll get a lot more power with it, and you can see everything that is going on which makes tuning very easy.
With the OEM ECU, you are pretty much running blind.