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84 not starting after a long/hard drive + occasional/random strange idle (fuel problem?)

1060 Views 33 Replies 5 Participants Last post by  RedP85
Picked up my AT 84 L-Type on November 28th 2022 and have been on the road to going from fair condition to good condition ever since. I am happy and proud of the progress I have made so far, but the last couple of weeks have been puzzling. Here is the situation...

After acquiring the vehicle, checking it for safety and doing a full service I managed to get it to run well and even pass CA smog. After cleaning the EGR system and replacing the thermostat with an OEM one from Toyota I even managed to get the check engine light to stay off! I began driving the car for a few errands weekly, still using my other vehicle for most long days or long drives. One day after a 1.5 hour drive I parked, came back 20 mins later to start it again and no start. Cranks fine, smells like gas in engine bay, but will not start. I used my other vehicle instead, came back after a few hours and tried to start the Supra again. It started up a little limp but then it ran great after a few seconds.

After research I learned it might be the infamous "heat soak" issue; an electrical, fuel or air related problem. I started testing potential culprits.
  1. Battery passed, main grounds are good and secure
  2. Plugs, inline spark tester passed all six
  3. The air flow meter passed resistance and physical inspection beneath cap
  4. Main relays 1 & 2 passed
  5. Circuit opening relay passed
  6. Solenoid resistor passed
  7. Start injector time switch passed
  8. Water temp sensor passed
  9. Ignition coil passed
EDITED* I figured out how to test the coil after a closer look at the wiring coming from the bottom I found the brown wire and ID'd the proper terminal. [I went to go test the ignition coil and could not find the positive (brown) terminal as described in the TSRM. Mine appears to only have a negative (black) terminal. Where is the positive terminal located?]

Distributor rotor, cap and cap O-ring are new OEM from Toyota directly. Plugs are new NGKs installed in December. Wires are new 10mm OMLs installed in January. The problem persists with these new parts and with the old parts that the car came with.

This problem does not seem to occur if the engine is only off for a minute or two. Said differently, if I take the car out for a long drive and shut it off for less than 2 minutes or so and then try to start it again it fires right up. But if I let it sit for 10 or more minutes it will not start and only fill the air with the scent of gas. No gas leaks on the ground or on anything that I can see. The scent appears strongest near the EFI housing.

I have not yet tested fuel pressure and compression as I do not think I have a low-pressure condition or a compression issue since it smells like gas and when it runs it runs great. However I am considering it could be a fuel line over-pressured issue so I may do this test soon.

The other thing happening, and this might need to be its own thread but I am concerned it is related so I wanted to include it, is what I am calling an occasional "strange squealing idle" for lack of better knowledge of what it is. Engine starts but immediately begins making an unbearable squealing and grinding sound while in P. Then when I move the shifter to R, it stops and starts idling fine. I can even drive the car in reverse with no issues or strange sounds. Moving the shifter to N or D kills the engine. Moving it back to P RESTARTS THE ENGINE!?!?!? Yea... it restarts the engine then goes right back into the strange squealing sounds until I put it into R again. When this happened I had to do a lap around my block in reverse just to get the car back in my driveway... I got a video of this happening because it was just so weird. Showing the video to some mechanics they said it might be the neutral safety switch going out. This issue has only happened twice so far but to make it weirder, the second time it happened it was D that would function instead of R like it was in the first time. Could this be an ECU problem?

Any advice on how to proceed with identifying what is causing this/these problem(s) is a greatly appreciated as I am hoping to approach this strategically to save time/money.
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Check fuel pressure regulator, heat soak maybe reducing the fuel pressure on restart after it sits for several minutes.
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