FWIW: According to this forum the Black Top ECU can suffer from a transistor meltdown from excessive cycles without the transistor being able to dissipate the heat. While their English language skills may not be the best their logic makes sense to me.
Typical Problems of Toyota Corolla Levin / Trueno AE111 20v MAP ECU (aka blacktop)
The bottom line is, if your BT doesn't seem to be making the kind of power you think it should (doesn't seem like the VVT kicks in) open your ECU up and look at the transistor pictured. If it's blown replace it or have it replaced and put a heat sink on it.
Since a transistor is a proportional switch (very simplified) if switched too fast - too often it can easily build up too much heat leading to burning up the transistor.
This might or might not be a problem, but thought it worth pointing out. Has anyone on this forum seen this problem?
I'll be checking my ECU in the next few days to look for the transistor in the photos.