I have found Toyota wiring harnesses to be terrible. I'd try the following: jumper wire power directly from the battery to the ECU & jumper a ground right from the battery to the ECU & see how it starts. If this makes a difference then you have a wiring problem. If it doesn't, try advancing the timing while cranking. If advancing the timing makes starting easier, then it's an electronic part beginning to fail. I have found that advancing the timing usually will let the engine start, but then it runs terrible because the timing is to far advanced. Once the timing is put back to spec, the engine starts hard or not at all. I have found this a few times. Replacing the distributor fixes the problem- good luck.