Hey Mate
sorry to see your having some bad problems
Ok i have seen this problem before on a mr2 when i went to map it the car was running just the same as your, Badly overfuelling and would barely run every so often. I spent ages checking for vac leak and bad components just like you are and what it was is there is a spider earth which is normally underneith the inlet manifolds on toyotas. This is the ground for the ECU and the sensors in the engine bay. Now there are more but the only one i exspect you have touched around that area is this one. Basically it was not tight and had got dirty and was causing the car to run like crap. I would suggest you check all the earths round the engine bay and the ones by ecu.
If you have no luck then give me a shout i have a spare 6sp ecu as you could have killed a resistor in yours when wiring emanage up as the ecu connectors are not great and you could have moved one.
I also have a spare powerfc ecu available to me which i could plug in and instantly tell you where the problem is as can view all sensors and controller everything