Truck STALLS when coming to a stop

[Monty in Calgary]

2006 Ford Ranger Sport, V6, 3L, 2WD, Auto.

The thing STALLS on me, intermittently, when I stop. Usually around 40% of the time (estimate)

Here's what happens:

I'm driving along all fine and good, until I have to do a Stop and Go, like at a stop sign, or a red light. When I'm almost at "stopped", it seems like the transmission wants to keep pushing the truck, and won't allow the truck to just idle, like normal, and then it SHUDDERS and STALLS! It's almost exactly what would happen if it was a manual transmission and trying to come to a stop, in gear, and not using the clutch. Starts shuddering, RPMs drop, and she stalls.

Once this happens, I have to put the truck into Neutral or Park, turn the ignition key all the way to off, then start the truck again. It starts and I'm able, then, to put it into drive and carry on. It's like the key turning off, then on again, kinda "Resets" whatever is wrong.

More info: I've tried shifting into Neutral as I'm nearing the stop when it feels like she's gonna stall... So I COAST to a stop. That will recover the RPMs and allow me to stop with the truck idling, but if I then put it back into gear, the stall process continues from where it was before going to neutral. So, even when I coast to a stop in neutral, I can't go again unless I turn the key off, then restart the engine.

Also, I've noticed that it doesn't seem to be affected at all in REVERSE gear.... just a DRIVE gear.
Also, I've tried hitting the O/D OFF button. No effect.

I've been doing a LOT of reading. Lots of stuff about how the Ranger uses a series of sensors that feed a main computer unit that controls stuff, like this IAC thing that is there to control idle and idle rate.

The thing that has my biggest interest is the Torque Converter Clutch. Have a look at the article in this link:
https://www.freeasestudyguides.com/automatic-transmission-tcc-torque-converter-clutch.html

Where it discusses about what it does, it almost perfectly describes what happens to me. It seems to be that it's supposed to put the transmission into a kind of Temporary Neutral and that if it doesn't kick in, it'll force the vehicle to stall.

A buddy of mine is a mechanic who works from his garage at home. He and I went out for a test drive today and, guess what... it WOULDN'T STALL! Crazy. (Normally, in the drive we did, I'd have expected it to stall at least 3 or 4 times!) Put the code reader on it... no codes except one that identified a startup problem. He thinks that's a coil pack problem. Tomorrow, I'm getting new plugs, wires, and coil pack (and fuel filter). Also, he's gonna drain the tranny fluid and replace, along with a new filter. The fluid is pretty dirty, but didn't smell burnt, so happy about that. He suggests to do these things (which needed doing anyway) and that this "MAY" also fix the stalling problem, thinking that the current tranny fluid may have lost the required properties to make the Torque converter clutch work properly, and hoping the new fluid might fix it. If it doesn't, then he figures the Torque Converter (clutch) is the next thing to look at, but to do this first. From our little drive, he's also satisfied that the transmission, itself, feels and acts healthy.

Anyway, I think that's about everything I can think of to describe it to you. Have a good ponder and, please, feel free to offer any suggestions, places to look, ideas.... whatever. Any questions, also, please ask. I'll answer whatever I can.

 

[RonD]

Yes, reads like the torque converter is staying locked, could possibly be the TCC solenoid but should set a code
Most likely its the torque converter itself

The shifting to Neutral disconnects rear wheels from engine so engine shouldn't stall if its a torque converter/trans issue, which is the case from your tests
So not an engine idle issue

Torque converters "normal" state is unlocked, thats what allows engine to idle in Drive, if you take your foot off the brake while idling on level ground vehicle should move forward at maybe 5-7mph but if you apply brakes again vehicle will stop and engine RPMs should stay the same

Torque converters have had locking for alot of years before computer control, its called Stall Speed, usually its near engine peak torque, so 2,500-3,000rpm depending on engine it was made for, and they still have this
But this locking occurred so late in RPM range it caused very poor MPG in automatics vs manuals

When electronic controls were first used TCC(torque converter clutch) was the first solenoid added
So computer could cause torque converter to lock earlier when driving, improving MPG alot
Its possible your TCC solenoid is the issue but that would for sure set a code

P0740 Torque Converter Clutch Circuit Malfunction
P0741 Torque Converter Clutch Circuit Performance or Stuck Off
P0742 Torque Converter Clutch Circuit Stuck On
P0743 Torque Converter Clutch Circuit Electrical
P0744 Torque Converter Clutch Circuit Intermittent

You do need a code reader that can read transmission code, most can't

If the valve itself is stuck then it may not set a code, but long shot on that one

 

[Monty in Calgary]

Thank you Ron. Appreciate the pretty detailed reply. Sounds like you're leaning heavily the way I am/was... "Something" to do with the Torque Converter, or Cluth, or solenoid. (No codes, so likely not solenoid).

Well, looks like I have no option, now, but to get down to a transmission shop, tomorrow, and see if they can accurately pinpoint the cause. Wish me luck!

 

[RonD]

Torque converter is the "clutch", but yes, I would guess you need a new torque converter

 

[Monty in Calgary]

Entire transmission was pooched. Full rebuild was necessary.

 

[RonD]

Bummer

 

[Dirtman]

Buy a new one!