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

Tiny
HADIA
  • MEMBER
  • 1990 TOYOTA 4RUNNER
  • 170 MILES
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.
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Wednesday, February 22nd, 2012 AT 8:35 PM

31 Replies

Tiny
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  • MECHANIC
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I see you've verified that the pressure regulator is working, but have you checked the actual fuel pressure yet?
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Wednesday, February 22nd, 2012 AT 10:18 PM
Tiny
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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?
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Wednesday, February 22nd, 2012 AT 10:37 PM
Tiny
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You can rent or borrow a fuel pressure gauge at most chain parts stores, like Advanced, Autozone, and O'Reilly.
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Wednesday, February 22nd, 2012 AT 11:05 PM
Tiny
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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.
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Sunday, February 26th, 2012 AT 9:02 PM
Tiny
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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.)
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Sunday, February 26th, 2012 AT 9:19 PM
Tiny
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Have you checked for vacuum leaks? Also check and clean the IAC and EGR, if so equipped.
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Monday, February 27th, 2012 AT 6:20 PM
Tiny
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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.
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Monday, February 27th, 2012 AT 7:53 PM
Tiny
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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.
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Monday, February 27th, 2012 AT 11:15 PM
Tiny
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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.
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Monday, February 27th, 2012 AT 11:43 PM
Tiny
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Ok. We'll be here.
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Wednesday, February 29th, 2012 AT 10:42 PM
Tiny
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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?
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Monday, March 26th, 2012 AT 7:03 PM
Tiny
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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.
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Tuesday, March 27th, 2012 AT 6:12 AM
Tiny
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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?
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Tuesday, March 27th, 2012 AT 3:32 PM
Tiny
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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.
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Tuesday, March 27th, 2012 AT 9:37 PM
Tiny
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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?
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Wednesday, March 28th, 2012 AT 12:31 AM
Tiny
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Yes. It's the one most often used.
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Wednesday, March 28th, 2012 AT 2:13 AM
Tiny
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You may be able to use carb and choke or brake cleaner to check for vacuum leaks, also.
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Wednesday, March 28th, 2012 AT 2:14 AM
Tiny
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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.
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Monday, April 9th, 2012 AT 10:43 PM
Tiny
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An you apply vacuum to it to test it?
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Tuesday, April 10th, 2012 AT 3:10 AM
Tiny
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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.
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Tuesday, April 10th, 2012 AT 6:44 AM

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