Been having this ongoing problem. I just got the truck back from an oil change and routine service from my Toyota/Lexus mechanic and pointed the problem out to them. They had the truck for 3 days or so but couldn't help me because they said they couldn't replicate the problem I explained to them.

The truck has fairly new (within 15k-20k) NGK platinum spark plugs and wires. During my recent service the mechanic also ran one of those smoke machines to check for leaks in all the vacuum lines (EGR was leaking and was replaced; nothing else was or is currently leaking).

The problem is that the truck will have a very low and rough idle and then stall out, and does so under these very specific conditions: engine warms up to operating temperate (drive to work, for example); then sits for approximately 30 mins. (stop for a bite to eat, for example); then attempt to start.

The engine starts up from cold flawlessly every time. If I let the truck sit for longer than an hour or so, it starts fine every time. If I stop for shorter periods of time - to get gas or something similar - it starts back up fine.

I have "checked" the 30 min. scenario several times and it never seems to fail. I replicated this problem 3 times yesterday throughout the day and night. Any and all help is greatly appreciated.

 

Have you tried starting it in flood mode(start it with the gas pedal to the floor once it starts let off) when its been 30 min? Give that a try and lets see if we cant narrow it down.

 

No, I have not, but will do so tonight after I get home from work (this is one of the "test times" I tried yesterday).

If it DOES start with no problem in flood mode as you suggest, what would that mean?

 

I don't know if your truck has it but on the 22re/rte they had the cold start sensor which caused me all sorts of problems with too much fuel on warm starts and chokes itself out. If it doesn't start at all then we aren't looking at too much fuel in the motor. Here's another idea. If you start it and it doesn't run try holding your foot on the pedal for a few seconds then let off. If it starts up we'll know its not getting enough fuel. This will at least eliminate two potential possibilities. If it isnt either then we have to look at other problems ignition or air.

 

It sounds like a fuel mixture problem caused by a temperature sensor problem. Here's what I would speculate is happening.
- When truck is cold, sensors give "cold" signal to ECU, ECU provides cold-start mixture, and it starts.
- When truck is warm, sensors give "warm" signal to ECU, ECU provides hot-start mixture, and it starts.
- When truck has sat for 30 minutes, engine is still warm, but sensors mistakenly tell ECU it's cold. ECU provides cold-start mixture to the warm engine, floods the engine, and it doesn't start.

Back in the days of "automatic" chokes, this was a common occurence. After sitting a short period of time (20-30 minutes) the choke temperature sensor would cool off and close the choke even though the engine was still warm, and it would flood. The fix was to take off the air cleaner and prop a block of wood in the intake to hold the choke open. Instant startup. I kept a small block of wood in my '72 Cutlass just for that purpose.

Unfortunately, that technique won't work for you, but the basic principle is the same. You need to find which sensor is lying to the ECU under the circumstances you describe. I would suspect the coolant temperature sensor as a likely first culprit.

 

Not sure if this is what you mean, but if I attempt to start the truck after sitting for 30 mins. it has the rough/low idle and starts to die, so I have to keep "tapping" the throttle to keep the engine running. At the same time, I quickly shift into gear and pull out of whatever parking space I'm in...once I start moving while in gear everything is fine and the truck runs as it should. But I must play with the throttle in these situations or else it will die and have a hard time starting up again.

And I assume that I would just replace this sensor and everything should be good from then on?

 

No, I wouldn't suggest you jump right in and start changing parts. I was just trying to steer you in a direction to start looking deeper.

Check this link out for the FSM.
http://personal.utulsa.edu/~nathan-b...sm/engine.html

Particularly look at the sections for MFI-System ECT Sensor, and MFI-System Troubleshooting. That'll tell you how to test the ECT (engine coolant sensor). If you can test it when the engine is acting up it might be instructive.

There are other possible causes, but this is one to look at.

And, if you don't have a hand-held DVM, get one. They're cheaper these days than almost any replacement part you can buy for our trucks, and with the info in the FSM, can save you a lot of time and cash.

 

I just tried this "flood mode" as you described and the problem was still present, so not sure what that means...

I will say, though, that the last two times I tested it (just now with the flood mode and earlier today when I got home from eating lunch) it started with the usual very low, rough idle, but never actually died out. Instead, it would idle low and rough for 20-30 seconds or so, and then "catch" itself and the RPMs would raise back up and it would be OK.

 

Could be a temp sensor issue. The best way to test that is get a laser temp gun and check the sensor's temp. Then get a resistance reading from the sensor before starting it in the morning and try to see if it is within spec. I do have to say that I did have a problem with my truck doing the same when I had the stock ECU still in. Once I got rid of it and went MegaSquirt I don't have it anymore so it may be a stock ECU bug.
Temperature（℃）/ Ohm（Ω）
–20 / 10000~20000
0 / 4000~7000
20 / 2000~3000
40 / 900~1300
60 / 400~700

 

Haven't gotten around to checking the hot/cold sensor as suggested earlier (hopefully will get to it over the weekend), but after thinking about this a little more is it possible that the truck may need a valve adjustment, and that is the cause of this problem?

I had a 1971 VW Bug - quite a different animal, I know - and it used to have the same problem...could never get it to start once the engine was warmed up. I remember the problem being that it needed a valve adjustment.

Was wondering if this could be the same case.

 

Any codes?

 

my guess is the ECT. http://ether3al.physic.al/93fsm-mobi...98engineco.pdf

 

No codes.

 

a valve adjustment on a 3.0 is very different from any other valve adjustment you will ever do. here is a link on the specifics on how to do the adjustment. it is not easy. and requires parts from the dealer if you need to change.


the valve adjustment starts on page 7 of this link
http://ether3al.physic.al/93fsm-mobi...e/64tuneup.pdf

 

Check the air intake tube from the air flow meter and the throttle body for air leaks.

 

I have a 92 same problem where might this temp sensor be located at I have the same model parts truck I would like to swap them