Short version:
If anyone is near 333xx (Fort Lauderdale area, Broward Co. FL) I'm willing to pay a tech who has a scope and knows how to use it, to solve this problem.

IT IS NOT A SIMPLE RESTART/START ISSUE.

Long version:

I'm the original owner, 105k miles, '85 Toyota Corolla GT-S with their "VAST" ignition and EFI system. Last year the car played a new game when I brought it down to Florida. Runs fine, chews up the interstate without a hiccup, starts hot or cold and restarts on the interstate with no problems. EXCEPT.

When the car has been parked overnight, and the ambient temps are maybe 85F or above, the car will crank but not start. Happened last summer, and I was waiting for a tow truck to bring it into a shop when I said wtf, today has been cooler...and of course it fired right up. Worked fine agin until this June when things got hot again--same "won't start from parked" problem.

I'd rather hire out than invest in a whole scope system to track down the problem. What I've gone through, last year and again this year, is most everything that can be checked without a scope.

The fuel pump whirs, I haven't bought and installed a pressure gauge to confirm that pressure is adequate--but expect it should be OK if the car can do a thousand highway miles without a hiccup. "Should", I know, no assumptions just best guesses here.

The starting system: Tested and bypassed the AFM switch, the EFI main relay, both sides of the COR (fuel cutoff relay), all of these test OK and when bypassed, there's power going to the fuel pump as verified at the pump harness connector.

The engine will crank and fire--briefly--but I can't keep it running. I think that indicates the engine is starting on the NE signal and then dropping out when the ECU should be switching to the IGt signal--but in theory, if the ECu wasn't sending IGt, the VAST system goes back to limp-home mode on the NE signal and runs anyway.

The ignitor pack, with connections to the coil and two harness connectors, has been removed, opened, eyeballed and tested with ohmmeter to make sure there are no cold solder joints, no breaks in the harness leads. That's not a functional test but again, it is all I can do without a scope.

So maybe it is a fuel pressure problem, more likely an ignition problem, either way I need to find a tech (or buy the scope, ouch!) to dig further. The local dealer uses ODBC now for everything, he's got one tech who will gladly toil away...for somewhere between one hour and two days, they guess. No scopes left there.

This is not a simple "won't start when hot" problem. Trying to apply logic here: The car starts just fine when it is cool out--even if the engine bay is at full operating temperature, i.e. 170F++. So logically nothing in the engine bay "should" be the problem. Which leaves the COR and ECU behind the glove box, and the COR tests fine. Last week I stuck the ECU in the freezer for a couple of hours to cold-soak it, no joy. Then there's the fuel pump--but I'd expect that gets hotter when sitting in tank with returned fuel warming it up on the highway all day. Or not?

Anybody in the area up for a challenge? I'm going to start the week looking for a fuel pressure gauge that can be installed under the hood, to reality check that fuel pump. But again...if it did a thousand highway miles without a hiccup?

PITA, my tools are up North, the car & I are forced to remain down south for a good deal longer, and the car apparently isn't happy about this.

Paging Sherlock Holmes...

fuel pump is highly unlikely to cause this symptom.
I would be looking at the IAC sticking shut (have seen this on an older toyotas, if this model has one)
and also the cold start injector as Bill said, and the coolant temperature sensor
these toyotas have a lot of TVVs and thermal switches all over - these are other areas you should be testing

doesnt sound like you would even need a scope - if anyone has a toyota capable obdI scanner it could likely be found within a few minutes!

most cases like this something simple is overlooked

spray some carb cleaner in the intake when cold to see if it starts

Another thought to ponder is if the ignition switch is operating properly.  This is a prevalent issue on some Honda's.  It is the temperature in the cabin that affects if it will start or not.

One way to try and verify the concern is run the vehicle with the heater on and the doors closed.  Then let it heat soak if it does not die and try to start it after awhile.

It will take a little more than that to confirm a bad switch but it might give some direction.  A start and die can also be a clue of a bad switch.

Sam

another but unlikely possibility is a casting crack - when it warms metal expands allowing a leak, When it cools down after sitting a while its full of coolant.

does the car use coolant at all?

have you checked for a leaking pressure regulator (gas in the vacuum hose)?

the IAC you asked about is like a choke on a carb - it allows air in for startup, and acts as a dashpot.

Also have you checked the Throttle body and make sure it is clean and not coked up. This is a VERY common problem with all toyotas.

Randy-
" does the car use coolant at all?" Uses about 2 gallons and keeps re-using it. Doesn't leak on consume any at all though.<G>

"have you checked for a leaking pressure regulator (gas in the vacuum hose)?" Interesting! Assuming that's vacuum controlled (I don't know offhand) that would be an easy sniff. But if it was leaking, no maintaining adequate pressure, then I couldn't run 80mph for four hours without some hiccup, surely? ??

Ditto the IAC, if that's always involved in starting, then my highway restarts should also have been a problem, no?

I'm not doubting--just questioning because I don't know.

"checked the Throttle body " Yes, in fact I'm rather PO'd at what is supposed to be a very good shop nearby. When I took it in to them last year--after it did restart while awaiting a tow--they blamed it all on the throttle bpody and cleaned that out. Totally unnecessary service, as the problem came back with the heat this year. So it has been cleaned out recently (i.e. 4000 miles ago) and made no difference.

Sadly I DO have a scope, a nice old bulky Tektronix that is a thousand miles away from me and not about to come visit. Pico seem to think I need their $1600 kit to do anything...I can't help wonder if a $400 older slower scope adapter and a couple or three probes would be enough for this car. After all, it isn't running a high-speed opto-digital data buss with a dozen CPUs and a hundred sensors all chatting away. Or for that matter a conventional scope...but I hate to buy a second boat anchor.<G>

The eventual turnout was that an AFM lead to the ECU had chafed at the firewall in a hard to spot connection. Sure enough, "something simple stupid!" as the startup circuit ignores airflow, and then the run circuit sees no airflow, the ECU was immediately shutting down the fuel and spark to prevent a fiery death.

No doubt in an OBDP-equipped newer car, there would be a trouble code for this. In this case, simply an ECU "decision" and no real way to hunt that down except for experienced hands and eyes running the harness.

That's the theory for now, we'll see if fixing that problem cured "the" problem when the weather heats back up again.

Car is humming like a clock. The guy who fixed it was full of (ahem) but whatever he actually did, he also fixed it.

I say he was full of it, because he told me how he replaced the 40A fusible link block. Which only exists on the carbed model of the car, for the carb preheat coil.