Those codes indicate that the TPS is shot (12 and 18) and that the OMP is shot (27)

It could just be the ECU though. Get another ECU from a s5 non-turbo and see. If you need another OMP, I happen to have one from my old s5 that I can give you.

Get a multimeter and probe the related pins for the TPS and the OMP at the ECU and compare the results with the FSM. If they are out of spec I would once again suspect the ECU is shot.

 

I believe it's the other way around.

Those are the exact same codes I had, turned out the OMP was bad which took out my ECU.

 

Don't keep plugging 'Good' ecu's into a bad MOP. You'll be sorry sooner or later.

Here is THE definitive thread on the situation in the entire forum.
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/s5-mop-ecu-failure-diagnosis-710938/

Please read the entire thread. This has all your answers.

Try testing the MOP. This testing protocol includes the FSM tests and extended tests. There is usually in internal short between the MOP coils that allows a reduced resistance to the output current from the ECU. This reduced resistance causes increased current which burns the circuits in the ECU.

You can have an MOP that passes the FSM tests yet still take out your ECU.