Why did my '99 4Runner stall?

[Spokaneman]

Outside temp is about 78
Gas tank is just below 1/4 full (but warning light is not on)
Car temp is at medium
Mileage is 194,000
Water pump and timing belt replaced at 140,000 (No other major engine work)

I'm stopped at a light, and the car stalls. I try to restart it, and it starts up immediately, and never stalls again.

My friendly neighborhood mechanic says that unless he can replicate the event, he has no way of diagnosing it. He said if I leave with him for testing, he could run up a huge bill and never find the result. His advice: wait until it happens again and see what might be the cause.

Any ideas of what happened or how I should proceed to get it diagnosed and repaired (if needed)?

 

[gamefreakgc]

IAC valve. When hot, sometimes it gets clogged and doesn't open, which cuts off all airflow to the engine at idle (throttle plate in closed position). It's the sensor and tubing that attaches to the bottom of the throttle body.

Clean your MAF sensor too. If it's gunked up as well sometimes it reads very little to no flow at idle.

 

[octanejunkie]

I have had the same issue/symptom but had replaced my IAC a little over a year and a half ago...

I have also had a bog (rpm drop) while driving at FWY speed randomly and intermittently which I thought was fuel related but I don't think it is

I believe my stall events and bog events are related, but had not considered the IAC... I can pull it tonight, what am I looking for, crud?

My MAF is clean

 

[LittleCaesar]

Wouldn't hurt to change the PCV too.

 

[octanejunkie]

Wouldn't hurt to change the PCV too.

Mine is new as of VCG job a few months ago

Sent from my Pixel XL using Tapatalk

 

[repo]

Mine does this too when I'm idling in D sometimes but it's rare. I feel like it seems to happen when the tank is getting low or I'm on a hill (I need to make a note next time). It starts right back up. No codes. I've never actually had a code thrown on this vehicle in 12 years... knock on wood... sometimes I wonder if computer is broken haha.

Throttle body and IAC was cleaned little while ago, gaskets and PCV/grommet replaced. O2 sensor, spark plugs and wires done recently. Most of the vacuum hoses replaced.

I noticed the connection where the rear PCV hose that goes to the driver side valve cover was quite loose where the plastic coupler goes into the intake hose. I tightened a ziptie around it to make it snug, I'll see if that does anything.

I'll test the coil packs tomorrow too. If they are good I'll replace the coil boots because they have 220,000 miles on them as far as I know.

Maybe the TPS? Or fuel pump?