1988 Nissan pickup Z24 engine (Callifornia version)

Question

1988 Nissan Pickup 4WD Z24 engine (California version). Can’t pass CA NOX test. EGR valve tested and is functioning normally. No vacuum from BPT to EGR with engine RPM at 2-3k. BPT Solenoid tests good. With solenoid connection removed, vacuum gets to BPT and EGR. Connect the solenoid and no vacuum. What controls the solenoid? I have been told the throttle position switch tells the ECU to break the ground to the solenoid. Is this correct? BTW by pulling the hose from the EGR to the bottom of the BPT exhaust gas does escape. Engine runs fine btw and passes everything except the NOX level. Watching the screen during the 15 and 25mph test I can see the level bouncing all over the place, but reads high on the readout.

What have you tried so far? (optional): First problem showed check engine light with EGR and Exhaust gas temperature sensor codes. Pulled, examined and reinstalled sensor and code for it went away. Found distributor cap cratered, replaced it and rotor and check engine light is gone. EGR system still not working correctly as described in question.

We have tested the throttle position sensor with the engine off and ignition on, the voltage jumps from zero to 11.5 v (not a linear progression) and the resistance (unplugged) goes from .3 to OL on the digital meter which to me means it's going open.
Disconnected cable reads 11.5v between contacts. There are only two leads going to the TPS.

What does the exhaust gas temperature sensor control? Why would any of these sensors cause the problem we're having and not show as an ECU code failure?