1990 Buick Regal No start/stalls when hot (normal max opera

1990 Buick Regal Custom 3.1 liter VIN T 123,964 miles. This problem is fairly long, so I'll try to keep it as short as possible. (BTW-This is my 81 year old mother's car, so she is at this point without a vehicle. This puts her in a very SEVERE situation. I'm paying for the parts, and repairing it myself, because she can't afford to have a garage repair it). I was driving Mom's car with Check Engine Soon-Trouble Code 32 displayed (EGR or EVRV (Evap canister purge solenoid/valve)). Car had slightly rough idle, but ran great. 3 weeks ago, I drove it (3 short trip errands, under 3 miles and 30 minutes) came home and parked it. Went out 45 minutes later to start it, and no start. Engine was still at hot operating temp. Finally got it running, drove 1 mile into town, and it stalled 2 times in that mile. Got it into town, where it finally shut down, and I had to have it towed. Checked computer, was showing Code 32 only. Removed EGR valve (Digital/Linear type (electrical, not vacuum)), and found plenum orifice completely plugged. Cleaned this out, and took apart the EGR valve, cleaned it, and put it back on. Car started, ran normal, and Check Engine Light was out. Drove it for about 15 minutes, and shut it off (at an auto parts store). Came out, would not start. I let it cool down for 45 minutes, and it started. Drove it home, and it died in the driveway (All with NO Check Engine Light). Got it into the garage, and checked the fuel pressure/fuel pump/fuel pump relay. Pressure was on the low side, but still in the factory specs. So I tore down the motor to the intake manifold. I replaced the fuel injector o-rings, new pressure regulator, new plenum gaskets, new EGR gaskets, new PCV valve/hose/grommets, throttle body rebuild kit, new o-ring on the IAC valve, and cleaned everything. Checked TPS resistance, was within specs. All of this was done to rule out the fuel system and vacuum leaks as the root cause. Car started easily, with a very smooth idle. Fuel pressure (pump and regulator) in dead middle of factory specs now. I let it idle for about 10 minutes, (to the hot operating temp.-The electric cooling fans did turn on), then it abruptly shut off, like I turned off the key. It didn't hesitate or cough, just simply quit running. It appears this is the problem: something is malfunctioning when the motor reaches the normal hot operating temperature (the elec. Fans do engage). I'm thinking it may be the ECT (engine coolant temperature) sensor, as this could cause the above symptoms, but I can't figure out why the cause of this problem is not setting a (the) trouble code(s) to indicate anything is wrong. I intentionally unplugged the IAT (intake air temp.) Sensor, and it DID trip Trouble Code 23. This verifies the self-diagnostics are working. In summary: SYMPTOM #1 Driving-Car won't start, or dies quickly after starting when engine temp. Reaches normal hot operating range (electric fans on). NO TROUBLE CODE(S) SET. SYMPTOM #2 Parked (at idle)-Car dies when engine temp. Reaches normal hot operating range (electric fans on). Fuel pressure in middle of specs. NO TROUBLE CODE(S) SET. Could a failing sensor/solenoid/valve operated by the PCM cause this without setting a trouble code? If so, which does it appear to be? I'm not completely convinced the EGR, MAP sensor, and EVAP (vapor canister purge solenoid/vavle) are the problem at this point. As I stated above, I'm becoming more convinced it's the ECT sensor. I'll pull it and check it within a couple of days. If that's not the problem, could it be something mechanical that does not set a trouble code? The water pump, thermostat, coolant (anti-freeze), and TEMP light and circuit all checked good. The engine does not appear to be overheating, so to me, this rules out the cooling system and hydrostatic lock-up. All electrical fuses and relays also checked good. I can fix the problem easily. If I know what the problem is. If any forum members have had this type of problem, please respond. I've spent over 3 weeks excessively worrying, and the sleep deprivation doesn't help matters any :) Thanks!