It pretty much as my rev2 turbo except for the following was connected on mine;

EVP

- canister purge solenoid
VTA2

- traction control TPS

(tied to VC)
THG

- as discussed, used for THE
TE2

- test connector
IDL2

- traction control TPS

(tied to gnd)
PS

- power steering
PSCT

- power steering
ABS

- ABS ecu

(no idea why as this is not present)
CCO

- catalytic converter temp sensor
ECO

- a/c economy mode switch

I think that the TE2 should be connected and THG tied to gnd.

The rest probably do not matter for your GT4 as I found some old notes which did not show them being connected for the Celica.
