New to the Forum. Sorry for the lengthy introduction.
Intro: I have a 1990 Toyota 4R, V6, SR5, 3VZ-E engine, 170K+. I have owned it since 1993 (almost 20 yrs). I have the original Toyota 4Runner Repair manuals and have always been able to maintain it myself with no major issues and over all it has been a dependable 4Runner except in Oct 97 the engine was overhauled by the dealer due to water leaking into the engine.
Current condition: It stalls at stop sign/light while idling (foot on brake & shift in drive). No shaking. If I just turn the car on put it in park or drive and keep it running even for ½ hour, it does not stall but if I drive it on the road for a mile or so and then stop at light, it will stall.
After the first occurrence, I found the intake hose connected to the throttle body was broken. I replace it and it worked for two weeks and then the problem reappeared. I removed and cleaned every part from the air filter housing up to and including the throttle body. It did not make a difference. Verified idle speed and timing OK. Checked all vacuum hoses, tested and verified as much parts involved in EFI and EC systems following repair manual instructions and using the limited tool/instruments I have. Nothing helped. Purred fuel injector cleaner in gas tank, it drove for 60 miles before it stalled again (and again). Took it to mechanics, they claimed faulty vacuum switch and they replace it and meantime killed my battery (total $350). It is now even worse than before. Can’t even drive it a mile without stall but The Engine light works but what is frustrating is that when it stalls, the Engine light never comes on and the ECU does not register any fault codes! When trying to read the any fault code, the Engine & O/D Off lights continuously flash at the same frequency for ever. Would like to replace the PCV valve but it seams that I have to disassemble half the parts under the hood to get to it! Any suspected part is about $100+ a pop.
Before I start spending any more money, any help/suggestion is truly appreciated.

I had an Acura MDX years back, similar problem ended up being a clogged fuel filter (so acura said anyways).

the location of the pick up tube can cause this, sediment will roll into the tube and block off the flow stalling the engine once the engine dies the fuel pump turns off and no more suction letting the sediment fall and allowing flow again.

Thanks for the comment. The Toyota does not suggest replacing fuel filter. They claim the fuel filter for this car is designed to handle a million miles. Toyota has removed any references to fuel filter in their Repair and Maintenance shop manuals and the filter itself is placed in a hard to access location. If anyone ever wants to replace it, they have to remove the car’s bottom support frame to get to it. Having said that, I have already bought the filter but I doubt it would fix the problem.

Thanks Bad Vision. May I ask which tube you are referring to as the pick up tube and connection is from where to where?

the pick up tube is located in the gas tank.
to fix the problem you will have to drop the gas tank down and clean it out well.
it also would be a good idea to remove the fuel filter and blow out the fuel lines with compressed air all the to the fuel rail. after you blow out the lines put a new fuel filter in they only are good for 2 years of use. no ands ifs or buts its good practice.
once the tank is cleaned and the lines are clear you should be all set to go.

i just noticed that you have a 2nd gen im not sure if they have inertia switches or not but you may want to check.

A clogged fuel filter usually doesn't cause a problem at idle, but rather under heavy acceleration. That's when the engine needs more fuel and the clog restricts flow.

The fuel pickup tube in the tank has a pre-filter on the end (frequently referred to as a sock).

EFI systems have a deceleration fuel cut circuit which might do it if it had a problem. A totally clogged EGR line could to. Just a couple things to look into.

My thought has been that if it is a fuel line clogging issue, the stall problem could happen any time ant at any point of operation (Ex., at start or while driving, etc...). The car has stalled on me at least 3 dozen times and every single time it has happened while I am stopped at stop light/sign. So my suspicion has been not necessarily on the fuel lines but other emission control hardware/sensors and vacuum lines. The fact that it does not register any fault code makes it more difficult and perhaps that is why the Auto Repair shop could not diagnose it properly either. Thanks for the suggestion. It will definitely be one of the things I would need to do.

You say foot on brake and shift in drive. I'll take the shift in drive part as it being an automatic.

Try driving in 1st and then come to a stop. And or drive in D, then shift down even though it's an automatic to 3-2-1. See if you can prevent the stall that way. Or what about if you give it gas to keep the RPM up while you are stopped even with foot on the brake?

I had a car once that would do a very similar thing. Problem ended up being that the automatic transmission was not shifting back down, or at least back down to 1st when I can to a complete stop. So as long as I drove it did not stall. If I kept it in 1st and stopped it did not stall, and if I manually brought it down from D to 1st or gave it a kick of gas I could often prevent the stall.

Was a selenoid in the transmission. Or at least that is what I remember the transmission guy called it. But I went to a place that pretty much only did transmissions and after a bunch of research, every other garage including the dealer wanted to change everything else except that. Even after I told them specifically that is what I wanted them to look at.

It may even be your mass airflow sensor. Mine had a similar problem a year ago. When I'd push my clutch in or throw it in neutral, the rpm's would drop and it'd stall out. Ended up bein that sensor, which I replaced with one in a junkyard (sensor,paddle and all), and bingo, problem solved.

I know this will sound crazy but my 87 22re auto was doing same thing. After
changing auto tq, both auto selenoids, mas, complete tune-up, ecm , etc,
cleaning fuel system still would die at stop/lights as long as idle was below 1200rpms. Finally took it to my uncles buddy and 2 days later it was fixed.
The problem was the EXHAUST VALVES were too TIGHT. Don't know if this
will help but maybe it will. Good luck

WHOA! Now that's knowing your way around a vehicle! Wish I could find a mechanic like that around here, to help when I get jammed up on something. Sounds like my best friend where I used to live--he solved a fueling problem by checking for solder cracks on the main relay with a magnifying glass--after a couple spots of solder, the fuel pump ran perfectly! Not many people would know to look for THAT.

Thanks for everyone’s advice. As we can see from this discussion, everyone participating has experienced the same problem one time or another but each came up with a different fix/solution. I will look into all possibilities discussed and will post an update, hopefully soon. Thanks.

It has been awhile since last I made a post. I have done a lot since then but the truck still stalls.

So far have 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 and the problem still exists. Recently I did fuel pressure test and engine smoke test.

Checked fuel pressure. Results are as shown below:
Switch to ON: Measured 46 psi (Spec: 38 – 44 psi)
With vacuum disconnected from pressure regulator and plugged, engine started:
Measured 46 psi (Spec: 38 – 44 psi)
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)

All measurements are at the highest limit of spec. (does this mean the pump and filter are in good shape?)

Performed smoke test to find any leaks
With engine off, 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.

If any one has any comments or suggestions on the fuel pressure and smoke test results I appreciate you sharing it with me.

So far I have spent $898. If the truck could make it to the dealer I would drive it there but it is 18 miles away and it will not make it there. I do not trust the local mechanic shops because they would not have the time to do the drive test this problem requires.

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)

by what you said here it leads me to believe the brake booster has sprung a leak the diaphragm inside this holds vacuum really well. i took my brake booster off tonight and my truck hasn't run for a week and when i pulled the brake booster line it hissed.
check the grommet to make sure its sealing well then pressure test that booster if the booster is leaking that will cause all kind of havoc.
this is why i recommend you always do the brake test with the engine running push the brake pedal repeatedly if your idle changes or suffers you have a brake booster leak. in most vehicles it wont cause a issue but if the leak gets worse it will cause idle and running issues.