truck stalls when engine hot (after 15 min of driving 45+mph) and then slowing down or idling at stop sign

1990 TOYOTA 4RUNNER
170 MILES
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HADIA
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It always stall when same conditions exist (engine hot, slowing down or idling at stop sign. (this can't be called intermittent problem)so why no code is recorded for this problem?

The very first time it occurred, I found the inlet hose connected to the throttle body was cracked. Replaced it and it worked fine for 2 weeks and then it kept on stalling.

Engine light works, reports other faults (disconnected O sensor, it was detected, error code was recorded and I was able to read the code from engine light)

Verified and adjusted idle speed (Cold start 1700, gradually rpm drops to 800 in park and 600 in Drive). Timing is set to 10.
PCV is has been a major suspect but the location makes it unreachable unless half parts under the hood are removed but I did heat up the engine and sprayed Throttle cleaner in the valve a few times with no results.

So far done the following:
Used Fuel Injector cleaner and it run fine for 60 miles before it stalled. Inspected all related hoses, cleaned air inlet path, Verified functionality for canister, Dash Pot, Pressure Regulator, EGR Modulator, VSVs and Check Valve per Toyota Shop repair manual instruction. Removed, cleaned and reinstalled Throttle body, Mass Airflow sensor, and EGR valve. Replaced Spark Plugs, Oxygen sensor and Catalytic Converter. Won't make it to the dealer (too far) so I took it to local auto repair shop. They replaced vacuum switch and also killed my battery in the process (total $350) and still problem exists. I have owned this truck for over 20 years and depend on it. Please help!
So far I have spent $787. If my problem is resolved I will most definitely donate to this site.
Feb 22, 2012 at 8:35 PM
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RIVERMIKERAT
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I see you've verified that the pressure regulator is working, but have you checked the actual fuel pressure yet?
Feb 22, 2012 at 10:18 PM
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HADIA
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Thanks for the reply. No I have not. It could be that it may require another tool to buy and I hesitate to spend any more money unless it really helps. If this test can be done with minimal cost please provide instruction and I will give it a try. For my knowledge, may I ask how (technically)the gas pressure would cause the stall at the situation I am explaincing? And also, why no fault code is recorded?
Feb 22, 2012 at 10:37 PM
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RIVERMIKERAT
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You can rent or borrow a fuel pressure gauge at most chain parts stores,like Advanced, Autozone, and O'Reilly.
Feb 22, 2012 at 11:05 PM
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HADIA
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To test the Fuel pressure on this 4Runner, the fuel gauge tester requires Banjo fittings and banjo adapter. Unfortunately I can neither find one tester set equipped with these parts to rent nor to buy locally. If I was sure of these parts' size specification I would buy them separately from hardware store. If I find a gauge set online, I would not know if the adapter and fitting that comes with it will be the right size for my needs. Still searching.
Feb 26, 2012 at 9:02 PM
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HADIA
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Still, if anyone out there can tell me what conditions would make this stall problem not to be picked up by ECU as a fault I appreciate it. (knowing that ECU can report other faults.)
Feb 26, 2012 at 9:19 PM
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RIVERMIKERAT
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Have you checked for vacuum leaks? Also check and clean the IAC and EGR, if so equipped.
Feb 27, 2012 at 6:20 PM
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HADIA
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As I wrote in the introduction of this thread, among other things, I have inspected all hoses, replaced vacuum switch, removed and cleaned EGR and Throttle body. In this car, I believe the IAC is a build in part of Throttle body and not sure if it can be removed as separate part. The Toyota repair shop Manuel does not mention IAC separately and an internet search for an IAC for this truck ends up with "no results found.". If I am wrong please let me know.
Feb 27, 2012 at 7:53 PM
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RIVERMIKERAT
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The why no code question is probably because the problem isn't bad enough to cause engine or emissions system damage, just driveability issues.

I don't see where you say you've checked for vacuum leaks, just checked a 'switch' for operation. That doesn't say whether a vacuum leak, which can cause your problem, is present.

Not being able to test the fuel pressure also hurts the ability to diagnose this type of problem. If the pump isn't delivering enough pressure, you can experience vapor lock after the engine compartment heats up. This is where the liquid fuel boils and vaporizes in the fuel lines, and is no longer able to be pumped through the system.
Feb 27, 2012 at 11:15 PM
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HADIA
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I have checked all vacuum hoses and other hoses related to EC and EFI systems for wear and tear, cracks and brakes. I have performed any vacuum test that the Toyota Shop repair Manuel calls for (not requiring any special tool except a vacuum gauge).
Of all this work, the vacuum switch is the only thing that Auto Repair shop diagnosed and replaced.
One way or another I will test the fuel pressure and report the results.
Feb 27, 2012 at 11:43 PM
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RIVERMIKERAT
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Ok. We'll be here.
Feb 29, 2012 at 10:42 PM
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HADIA
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Sorry for late reply.
I finally bought me a Fuel Pressure gauge with correct Banjo fitting and tested the pressure with the following results:

Switch to ON
Measured 46 psi (Spec: 38 – 44 psi)

With vacuum hose from pressure regulator disconnected and plugged, engine started:
Measured 46 psi (Spec: 38 – 44 psi)
Note: Keeping the vacuum hose plugged or not plugged did not make a change in readings!

Vacuum hose reconnected and engine idling:
Measured 39 psi (Spec: 33 – 37 psi)

Engine stopped:
Dropped to 21 psi and within a couple of seconds drops to about 5 psi. (Spec says that it should remain at 21 psi for 5 minutes after the engine is stopped)

Firstly, these readings are on the high end of the spec (and slightly more).
Secondly, after the engine is stopped it does not hold the 21 psi for long.

Question: Since the reading are high, does it mean the fuel pump and fuel filter are in
working properly as they should?
Mar 26, 2012 at 7:03 PM
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It sounds like the filter and pump are working. But, it sounds like the check valve in the pump has failed.
Mar 27, 2012 at 6:12 AM
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HADIA
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Thank you. Before I mess with the check valve, theoretically, would check valve failure create the condition that would make the 4 Runner stall while idling at stop light, or is this just another issue with my 4 Runner?
Mar 27, 2012 at 3:32 PM
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It depends on the type of failure with the check valve. It could be experiencing an intermittent failure where it isn't allowing enough pressure to the injectors occasionally, and not holding pressure properly.
Mar 27, 2012 at 9:37 PM
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HADIA
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Thank you again. I assume the check valve is part of the pump and therefore per your diagnosis, the pump needs to be replaced. I will look into this. So far, $846 and going up.
Though I have checked all I could for vacuum leak, I wish I could find an easy and inexpensive way to smoke test the car for leaks before anything else. If I was to do a smoke test for leaks, where would be the best point of smoke entry. Someone suggested the brake booster vacuum hose. Is this an ideal point of smoke entry?
Mar 28, 2012 at 12:31 AM
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Yes. It's the one most often used.
Mar 28, 2012 at 2:13 AM
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You may be able to use carb and choke or brake cleaner to check for vacuum leaks, also.
Mar 28, 2012 at 2:14 AM
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HADIA
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Sorry for long intervals between reply. I work on the truck whenever I get a chance and today I smoke tested the vacuum lines using my homemade smoke machine (A 12v air pump, a pickle jar, a few fittings and pieces of tubes and some mosquito repellent coil). The only thing I had to buy was the repellent. Sealed the air filter and introduced the smoke through the brake booster vacuum hose. The only smoke I witnessed was from under the cap of the EGR Vacuum Modulator and from around the Mass Airflow Sensor. Inside the Modulator cap there is a small filter and still in place. Is it possible or expected that because the engine is not running and the EGR Vacuum is inactive therefore the smoke backs up in the Modulator and leaks out? Any comments or suggestions?
Note: I tried to take a few pics but unfortunately, the smoke was not visible in the photos.
Apr 9, 2012 at 10:43 PM
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RIVERMIKERAT
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an you apply vacuum to it to test it?
Apr 10, 2012 at 3:10 AM
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HADIA
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No vacuum applied. With engine not running but ignition on ON so that I can run the pump, I pumped smoke into the system to find any leaks. Smoke appeared from under the cap of the EGR Vacuum Modulator and from around the Mass Airflow Sensor.
Apr 10, 2012 at 6:44 AM
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HADIA
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Just an update. I reached my limit of spending ($1K) on the truck for now. The truck has officially been put in hibernation. Someday I will tow it to the dealership. In the meantime, I feel like a disabled person who has lost his wheelchair.
May 21, 2012 at 5:05 PM
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I don't think smoke should have been visible. You might try seeing if the seals or gaskets around those 2 parts can be worked on and fixed.
May 21, 2012 at 10:23 PM
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HADIA
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Out of hibernation and back on the road again!
As you all recall, my truck would always stall while idling at stop signs and stop lights.
Running out of options, I played around with Throttle control sensor to see if it would effect idle performance and hopefully stop the stall problem. This action recorded two engine faults.
A) Throttle Control Sensor Fault,
B) Engine Coolant Temperature Sensor Fault.

Set back Throttle sensor to original state and the error for this sensor went away but from here on, the Coolant temp sensor fault persistently remained. I replaced the Engine Coolant Temperature Sensor (ECT) and Halleluiah! I have driven it for 100 miles since and no stall and it passed California’s strict smog test beautifully. After spending $1300 replacing and or cleaning many parts, a $13 sensor fixed the problem. For 8 months that I was dealing with stall problem, the truck neither generated an engine fault nor the temperature gauge indicated anything other than the normal driving temp until I messed with Throttle control sensor. How and Why!? Well, at this point I don’t care.
In any case, thanks to all those who made suggestions and recommendations.
Sep 8, 2012 at 7:27 PM
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RIVERMIKERAT
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Hadia, congrats. California's smog laws are the strictest in the country.

As to why the ECT would be bad but not generate any spurious or incorrect readings or any codes, that's one of those things that Toyota isn't telling anyone.
Sep 9, 2012 at 1:13 AM
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MSMITH4466
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My truck does the same thing when all warmed up it also bucks and gas gage goes to e I have changed every censor there is and still does it
Sep 9, 2015 at 5:54 PM
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HADIA
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If the gas gauge goes to E, I would take a closer look at the Fuel system. Have you replaced the Fuel filter?
(on the side: My truck is in hibernation again. After more than a year of driving smoothly, The fuel dampener is leaking gas. It is a less than $200 part but unfortunately it is cramped on the back of the engine, impossible to get to)
Sep 10, 2015 at 12:25 PM
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MMMDAVE
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I had to replace my leaky fuel dampener recently. Yes, it's a pain to get to. Best thing is to remove plenum. While I was in there, I replaced pcv valve. Ironically, that fixed the "stalling when hot" problem, which is why I subscribed to this thread in the first place ????
Sep 10, 2015 at 1:03 PM
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HADIA
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Thank you Mmmdave. Up to now I had not come across anyone who had to replaced the Fuel Dampener. I am not sure of your 4R but My Toyota 4R in 1990 model (3VZ-E engine). Firstly, I am short on vocabulary! By Plenum I assume you are referring to the air intake chamber. Because of the age of the car, and the fact that there are so many components hat have to be disassembled for this job, I have hesitated to start on this. I am scare of that one bolt or a nut that just may refuse to open or get damaged trying to open.
In any case, if you (or anybody else) can provide information on special tools if needed and the proper steps I have to take to replace the dampener I very very very much appreciate it.
Sep 10, 2015 at 2:10 PM
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MMMDAVE
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Mine is also a 1990 3vze. Lots of vacuum hoses. Get a roll of masking tape and a sharpie and label everything. Take pictures. All so you can put it back together right :-)

Get get a new plenum gasket, and a pcv valve before you start. You'll have to disassemble fuel lines and throttle linkage too. I'd advise doing it in a well ventilated space. Those gas fumes will get to you big time. I didn't use special tools, just a good set of socket wrenches mostly. The usual.

There may be a YouTube video out there that would be worth 10,000 words.
Sep 10, 2015 at 2:21 PM
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MMMDAVE
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Oh yeah, the plenum is the big silver thing that covers the top of the engine.

Good luck!
Sep 10, 2015 at 2:30 PM
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HADIA
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Thank again Mmmdave. By special tool I meant and was hoped there is a tool that would allow replacing the dampener without messing with the plenum. Any way, very busy now but I will plan and work on this and post the results though I can't tell when that would be. Regards.
Sep 10, 2015 at 4:20 PM