Car wont start cold and stalling at hot idle intermittent problem

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My car is in the signature. Its a 80s toyota that uses TCCS ECU with contactless distributor, with a flap type air flow sensor (like 22RE).
The ECU controls ignition timing advance so there are no governers and vacuum advancers in the distributor.

About a month ago I faced a hard starting issue. The engine was cold (ambient temp 30 C) . It cranked very strongly but wont fire up. I could smell gasoline fumes from the exhaust , that means fuel pump and injectors are working. I also confirmed the fuel pump was working. I then pulled up on the Air flow Meter cables (AFM). and it started right up. The AFM cables go from that side all the way across the engine front to the Intake manifold which goes to the ECU. The AFM, distributor, water temp sensor are all somewhat close to the front turbo "cool side". So after it started I did not think much of it, then I was stuck in traffic about 10mins later and the engine is already warm. Suddenly while idling with the car not moving, the engine cut out. There was no warning. No idle stumble, jerking or whatever. It just cut out. I quickly put the Trans in N, and tried restarting, it immediately fired up and I drove home the rest of 25km with no incident.
Now I am getting worried. 2 years ago I had this problem, I thought it was the AFM wiring is too taut with no slack, so I added 2" of wires to the AFM loom to give it some slack. For 2 years the problem has never showed up once, until now.
So it happened again a at least twice a week, out of 5 days driving. No other issues, no clues, the engine when coasting , accelerating, turbo boosting, all works great, engine never stalls when car is moving. My mechanic did the simple things first, cleaned the TB and all idle air passages, it drove 2 days with no issues, then it suddenly came back while I was outside of the car with it idling in P checking the atf level. Since I was outside of the car, I had to put the dipstick back and get to the drivers seat, so I lost about 20 seconds. The car wouldnt start, it cranked, but wont fire up. Gone through the whole 9 yards, testing fuel pump, it was ok. I suspect its not sparking, why , I dont know.
My mechanic is busy, I so I tried doing continuity tests over the weekend to check all the wires and grounds that go back to the ecu from the TPS, AFM, water temp sensor, since some of those wires are interconnected . All connections to ecu checks out good.
I also cleaned and sanded the grounds for this circuit, as well as the ignitor + ignition coil.
While trying to remove the distributor cap, I heard a cracking sound, and to my horror I saw that the cap was cracked near the mounting areas, all the way to almost where the lugs are, but the cracks dont reach the lugs, and the crack is clean, no oil, dirt, or water inside the cap. I am unsure If i cracked the cap or it was already cracked. I replaced the cap with a used one in my stock, cleaned up the contacts inside and re assembled.
I am unsure on how these older ECUs work, But I think its like this
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I am getting a spark tester and I will keep it in the car to test spark the next time it happens to confirm if there is sparks.
I also carry my multimeter around. If the next time it doesnt start and I dont get 5V through the Vc circuit that means the ECU has shorted out. Also,
as far as i know, the ignitor sends back confirmation signals that the spark is firing, I am unsure if it get this confirmaton from the distributor or the igniter itself, so could a bad distributor with no spark not send a confirmation causing the ecu to stop firing.

This is all very difficult to diagnose as these dont happen all the time. In summary, cold hard starts. Hot stalling. If hard start happens, stalling will follow later at idle. Immediate restart will get it started, if wait too long, wont restart, need pull AFM cables again then will restart. As far as i know AFM is not needed for starting except for the fuel pump pins which are intact and making good contact.
The one thing in common both issues have is, low rpm, idling rpm is low, and starting rpm is low. I also somewhow suspect the crank angle signals from the distributor, the low voltage circuit with 4 wires back to the ecu.
Yesterday (monday) was the first day driving after the wiring check and grounds clean up, no incident of hard starting and stalling. this morning, no incident also. The next start up as well as the next few days driving till Friday will tell if the problem is still there.
If any of you are well versed with the logic program of pre C.O.P toyota ECU please do share.
 
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Joined
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It sounds like there's an intermittent connection or short somewhere. Idle the engine, go under the hood and systematically move all the wires and connections to see if you can make it stall. If it dies, restart and move the same thing again to see if it's repeatable.

The problem with a problem like this is that you can test all you want while the car is working and it will all test perfect. You have to get the problem to occur constantly then test.
 
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Come on, your among friends. Don't just say 80'sToyota, tell everyone exactly what year if you want help diagnosing. It actually makes a difference in communicating your problem.
 
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Come on, your among friends. Don't just say 80'sToyota, tell everyone exactly what year if you want help diagnosing. It actually makes a difference in communicating your problem.
From his signature, I assume it's the 1989 Toyota Soarer GT Twin Turbo L. Not that I've ever heard of that before. Had to Google. It looks like a Honda Prelude. Very nice!
 

alcyon

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Come on, your among friends. Don't just say 80'sToyota, tell everyone exactly what year if you want help diagnosing. It actually makes a difference in communicating your problem.
Yes 1989 toyota Soarer. Uses a JDM only engine, the 1G GTE https://jalopnik.com/toyotas-first-twin-turbo-straight-six-is-stranger-than-1824260905
. Control wise very close to the 7M-GE. The ECU logic should be 95% the same.

1629208424164.jpg

Water temp sensor to ecu is under distributor, and the loom goes across the front of the engine. Pulling on AFM wires also moves the water temp sensor wires, oxygen sensor wires and distributor signal wires (G-,G1,G2,Ne)
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Joined
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A frequent problem of any ECU (or other control module) of that age is dried out or leaky capacitors. That is prone to cause intermittent problems. Preemptive capacitor replacement is a common thing on antiques.

I re-emphasize that you don't necessarily have to understand exactly how it works, first you need to get it to break down for long enough to identify where the problem is.
 

alcyon

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I had a 1983 Toyota tercel and it would cut out like that. Turned out to be a faulty igniter. Once it was replaced never happened again.
In your experience, it is the trigger below or the coil above that fails.

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alcyon

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Problem may be solved. After sanding the ground point shown
1630295666288.jpg

The problem hasn't return in two weeks straight. I am planning to change the negative terminal anyway because its heavily oxidized, but yeah for the last 10 days straight no hard start or stalling. I think this ground point is grounding the ECU sensors and or distributor cam signal. So when the voltage sent back to the ecu is weak (low rpm) , the ecu thinks the engine is not turning so it turns off the spark.
 
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