I will start off saying that my car runs perfectly about 99% of the time.

The simple way of putting it is that the engine takes spells of to want to go lean under acceleration. If it stalls during one of these spells, it tries to flood on restart. At first, this was a minor issue. But it seems to be getting worse.

It only does this under very specific conditions, detailed below. This is just really difficult to explain in paragraph format...

Conditions:
1) Happens within a very narrow temp range from just below full running temp to a few minutes after reaching full running temp. When the engine is cold, it's fine. Once it's been at running temp for a few minutes, it's fine.
2) Does not happen every time I drive, but randomly. Seems more prone if I haven't driven in a couple days, but not always. Less likely if I've driven it daily, but not a guarantee that it won't happen. This is the most infuriating part.
3) Moisture does NOT seem to have an effect. I had no problem yesterday, but DID have a problem today. It's been raining on and off both days. Though today is admittedly wetter.

Symptoms:
1) As you're driving, the car will act like the fuel mixture is lean under acceleration only. Pops, sputters, etc. Cruising is fine. If you feed the throttle in slowly, it's fine.
2) If you stall the engine, it tries to flood on restart. You have to hold the accelerator on the floor in "Clear flood" mode. It takes a minute or so of cranking to get it to restart.
3) Occasionally it tries to flood on a cold start, but this generally happens if I haven't driven the car in a few days. Ambient temp. doesn't seem to affect this. I've seen it start fine in temps ranging from 60 down to 20, and I've had it try to flood in the same range. Most days it starts right up with no problems.

I am thinking it's a temp sensor. I'm going to use a USB ocilliscope so I can datalog the temp, I just need to find the wire coming into the ECU from the sensor & a couple other things I want to watch (IAT, airflow, maybe RPM?).

I'm open to any other suggestions, though!

 

For the flooding when engine warm, make sure the cold start injector is not operating.

 

It only tries to flood warm when it's having an episode, not all the time. I do believe it's the cold start injector trying to flood it, but it has to be triggered by the ECU to fire. The ECU should only tell it to fire in a certain temp range. Unless it's getting a bad signal, it shouldn't fire warm.

The part that's got me confused is that it's going lean on average to hard acceleration during these episodes. If I take of really gently (gently enough to aggravate people behind me) it is OK. But if I get into it too much, it starts popping and sputtering and is likely to stall out. I've nearly been rear ended twice because of this (though it wouldn't have been my fault, still annoying.)

 

Most Toyota cold start injectors systems of the age used a separate coolant temp sensor switch. When the fuel pump relay was energized so was the injector timer. But the ground circuit was completed only if the temp sensor switch was closed.

The fuel system also has a VSV to increase fuel pressure at high temps and immediately after starting.

 

Oh, wow! As always, Joey P, You're my beacon in the darkness! If the system runs off of a second sensor, that just saved me tons of diag time !

Any good resources for schematics for these cars? I haven't had a chance just yet to pick up a Haynes manual...

 

The Haynes manual (Camry 83-91 #1023) has a schematic plus testing method.

See Private Message.