ECM or sensors or wiring

1990 olds cutlass Ciera, 3.3 lt fuel injected, ps, pb, auto trans, 90,000miles

PROBLEM: car ran fine, good performance characteristics. Park the car for the day. Next day, we go out to start, but no!

SYMPTOMS: turn ignition on, starter engages, engine starts immediately. It runs for maybe five seconds, then blaaaah. It stops as if the spark or fuel has been abruptly removed from the equation. If again engage the starter, it won’t fire. If you wait 20 minutes or so it will repeat the scenario.
Then one afternoon I found a plug that was not on it’s sensor. So I eagerly cleared my tools from the engine area, said a quick prayer and turned it over. Shazam! It ran and good too, the way it did before it fell ill. We drove it for a few days. Just short trips to the store or to friends houses. Then one day it did the same thing. First I looked at the sensor that made it work last time. Nope, still plugged in. Then I checked all the fuses.

Ahh! THE COMPUTER:
Ok, I did the cold computer test by leaving the ignition off and placing a jumper from pine 1 to 2. Then I turned the key. One – one two--- one – one two. Three times, then a long pause and next it signaled a 15 and then a 22. My Chilton’s did not list those codes so I got the GM data sheet off the net.

15 Coolant temperature sensor or circuit fault - signal
voltage high

22 Throttle position sensor (TPS) - signal voltage is low
Fuel cutoff relay circuit - open or shorted to ground

I thought it was the temperature sending unit first, so naturally I replaced it. It didn’t change a thing. Everyone over here thought it was the fuel pump or that system. It is not. With a pressure gage on the fuel rail return at pre-ignition it pumps up to 42 and stays put. While starting it drops to about 38-40. Then after the engine dies, It goes up to 42 as it was in the beginning. I have tested every wire in the fuel pump system. I have tested the relay switch and contacts. The one wire that I am having difficulty identifying is the yellow to the coolant temperature sensor.

QUESTION:
a. Will the computer continue to give a code 12 if one part of the computer is not working ok?
b. Which yellow wire belongs to fuel pump system.

When I try to start it, it sounds like when the starting system drops out there is nothing next (no open or closed loop).

QUESTION: This seems like an opportunity for someone who really knows to address the transition from start to run.

Thanks, Vern.