Unfortunately the 1G is a rare bird. It, like the 1JZ never saw North America but unlike the 1JZ it is not a popular engine. This site has become largely USDM and CDM centric and the resources you will find here are limited; I suggest trying UK, AUS and NZ based forums as the vehicle did make it to those markets (even if just as a grey market import). Perhaps BillUK may know of some resources for these.
Things I would start with checking are: diagnostic codes stored in the ECU, timing, air flow meter (isn't that a MAP based system?), speed sensor, igniter and coils, intake plumbing for leaks... then I'd start in on the transmission.
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