It's intermittent, but becoming more frequent.
2004 Supercab XLT, 4.0L, AT, 4x2, 202,000 miles: Stalls when coming to a stop. Does not cause "Check Engine" Indicator Light.
The longer driven between stops, the more likely it will stall. The stall is very similar to (in the olden days) of coming to a stop without using the clutch on a manual transmission.
Could it be the torque converter is going out to lunch on this thing?

Thanks guys!

 

Certainly possible but less likely than an issue with idle control or TCC system

Try shifting to Neutral when coming to a stop and see if engine RPMs still drop lower than expected, without the "load" if being in gear it most likely won't stall but may stumble before it recovers and idles correctly
If idle doesn't stumble once stopped shift back into D right way to see if engine stalls, torque converter still locked

There are a few codes for TCC(torque converter clutch) solenoid, this solenoid in the transmission locks torque converter at lower RPMs for better MPG and power
P0740 Torque Converter Clutch Circuit Malfunction
P0741 Torque Converter Clutch Circuit Performance or Stuck Off
P0742 Torque Converter Clutch Circuit Stock On
P0743 Torque Converter Clutch Circuit Electrical
P0744 Torque Converter Clutch Circuit Intermittent

You need a "better" OBD2 reader to see transmission codes in most cases, they usually turn on the CEL or OD OFF light will flash
But check for codes regardless

The Computer(PCM) has engine RPMs available and it can see transmissions input RPMs as well
When the PCM uses TCC solenoid to "lock" torque converter then engine RPMs and Input RPMs would be the same, no slipping, if there was slipping then P0741, if when slowing down and TCC was shut off, if the RPMs stayed the same then P0742, not unlocking
TCC was the very first solenoid added to Automatics, so lots of history and improvements, and not a hard system to monitor, lol, i.e. RPM matching
And you should get the P0742 code even if problem was not the TCC solenoid but was the torque converter

Absence of CEL or flashing OD light, and no codes, would tend to point to idle issue

 

Hi, Ron,
Thank you for your timely reply!
This is going to require someone else to deal with it because I have neither the knowledge nor tools to sort this one out.
Yes, shifting into neutral as it starts to stumble will prevent the full stall. Sometimes it will stumble with the RPM dropping to +/-400 revs before smoothing out. Sometimes the shift to neutral is all it takes to make it behave. Once at a full stop and idling smooth, dropping into gear, it acts normal again.
At the onset of this issue, it occurred rarely, about 3k miles ago. Since then, nearly all miles have been "city" driving with probably half of that being on freeways in the Phx metro area. As time goes on, the stalling behavior is more and more common and becoming probably half of the full-stop conditions.

I guess this will probably be another one of those $1k shop repairs.
Ah, but for the good ol' days before the introduction of computers into automobiles............

 

Just reads like IAC Valve is sticking closed , not hard to clean these, or just replace it, 2 bolts and a 2 wire connector, top front of engine so not even hard to get at, lol

 

Thank you for your input.
However, the Idle Air Control valve is new. Replaced about 1,500 miles ago. Probably not that.

 

If it wasn't a Motorcraft or Hitachi IAC Valve then could be that, so check the brand
And why was it changed 1,500 miles ago?

You should feel a lurch forward when stopping(if torque converter is locked) as computer tries to keep engine RPMs above target "in gear" idle, of 750-800rpms
Computer won't just "let the engine stall" it will let in more air, via the IAC Valve, to try and keep engine running

 

The IAC valve was changed for the same symptoms / issue but changed nothing (as I recall it was the NAPA house brand. Belkamp?). It has gotten progressively worse.
I do not have the computer/control module / electronics knowledge or expertise to diagnose this issue. I quit working on autos for a living in 1984. Once the ECM's get more sophisticated than the electronic ignitions of THAT time, it all becomes Greek to me.
I just have to pony up the dough, nowadays. It sticks in my craw because I feel like I am getting hosed, but that is just the way of the world these days, isn't it?

 

Hello, Ron,
Went and bought an INNOVA 6200P scan tool. The description says that it reads transmission codes/data.
I downloaded their "repair solutions2" app onto my phone.
Paired the device with the vehicle in accordance with the directions. Reads engine data fine. no engine codes stored. Cannot find any transmission menu or module in the tools. Unable to scan for transmission codes. I am stumped.

Ideas?

 

Maybe there are not any

Unplug IAC valves 2 wire connector and turn key on, then start engine, you will need to "give it gas" so it will idle
CEL should come on pretty fast
Shut off engine and read codes
Should be an IAC Valve code listed
P0505 Idle Control System Malfunction
P0506 Idle Control System RPM Lower Than Expected
P0507 Idle Control System RPM Higher Than Expected

This is just to check the "sanity" of computer and code reader

Code will self clear when you plug IAC Valve back in, or you can see if new reader will clear it

 

New Motorcraft IAC valve on order. Scheduled to arrive 6/22.
Dang, these things are expensive!! Was quoted $168 by Ford dealership. Found online at $133 delivered. Still expensive, but leaves me a little beer money.
Still cheaper than car payments, though!

 

UPDATE:
I replaced the Evaporative Emission Cannister Purge Solenoid because my research indicated identical symptoms if the solenoid is inoperative and I had already replaced the Idle Air Control Valve.
The symptoms continued to occur very sporadically after replacement of the purge solenoid so I ordered another IACV - the Motorcraft unit and then left on an extended road trip of +- 4.5k miles over a two week period. She stalled three times during the first two days of the trip and behaved quite normally after that. Maybe the extended road time helped? (I was driving 12-14 hours each day.)
Upon my return, the Motorcraft IACV was waiting for me so, because it is such a major undertaking, I spent the necessary 45 seconds to change it out - keeping the nearly new NAPA Balkamp unit for possible future need.
Through out this ordeal, the system did not throw any codes and that makes me wonder if the Evap Cannister Purge Valve was the problem all along... Guess I will never really know, but that is ok. All is well.

The old girl now has 206+k miles and is running and performing as designed and intended.

Many thanks to all who weighed in on the problem!
If things hold true to form, I will probably be back for additional support and advice!