As on-going investigation to figure exactly what has been done to my -99 FD Type RS, I checked my MIL codes via diagnostic post because I noticed MIL light was removed by previous owner.

By shorting the GND and TEN and then reading voltage between FEN and B+, I found the codes 32, 42 and 43 and reseting by removing battery, code 43 remained even before start.

So
- secondary air solenoid
- Turbo precontrol solenoid
- Turbo wastegate solenoid

Because car seems to function ok, decided to take a peek at solenoids under the intake as this pointed me to direction of some changes in vacuum system.

After removing the brace bar, throttle cable and pressure chamber I was greeted with this:


Disconnected solenoids..

FSM says those are the precontrol and wastegate solenoids, I don't have my upper intake gasket yet so didn't remove it yet, but based on the simplified vacuum diagrams, I should have boost controller somewhere?

Any idea where it could be? ECU is standard original N3G1 280ps ecu and theres no other splices in there except wires going to Pilot temp / fan controller and one splice of speed sensor going to the radio which I removed while in there.

I'm also including picture of the airbox hoses, so you could tell me if theres something funky going on in here:

 

The wastegate solenoid being disconnected is most worrying, Pre-control not so much as it's one of the changeover solenoids.

The wastegate solenoid being disconnected might offer an explanation for why the previous owner sold it. I don't have the 99-spec service manual, but the twins operate exactly the same as a 93-spec N3A1 setup, as does the 20B Cosmo.

The best thing you could do is plan for a vacuum hose job, using thick wall silicone hose. It will help you uncover the car's mysteries and you just might discover the wastegate/pre-control solenoid connectors, or at least some evidence of their absence (a cut branch in the harness, visible wires, etc) so it can be repaired properly with new pigtails.

Might consider relocating the solenoids as well. Doing so while performing the vacuum hose jobb is the best time. IIRC, a stock N3A1 FD requires 40ft (14 meters) of 4mm hose for the solenoids. Relocating them will add 10-15ft (3-5 meters). My 20b FC with the Cosmo twins has the solenoids relocated to the inner fender and I needed 50ft of hose to do this.