Car stalling coming to a stop

[lolford]

Hi, I have a 15 Taurus with the 6F50 that has stalled when stopping at an off ramp. This has happened a few times, but it's only when the car is fully heated up. If it doesn't stall the RPM will dip for a second down from the 600 idle, to 350ish rpm then recover. When it stalls I can start it up right away as if nothing happened.

I took it to a transmission shop and they said it was a failing torque converter. It was replaced and aside from shifts feeling a bit nicer the problem is still there. The weird part is it only happens when the transmission is fully up to temp!

The shop is suggesting to replace the valvebody and solenoids though there are no codes.

I'm not really sure what to do next as the issue has been going on for years, but I've already spent a bunch so I'm hoping to fix it.

 

[hemitom]

I had this happen twice in my mkx with 3.7 but a little different .
Fully warmed up slowing down to stop ! would run as if missing service AWD warning would come on then stall it would restart and run fine. Cleaned throttle and so far hasn't returned in the last four months .

 

[The_Jeff]

This is actually kind of common though I've seen it more on GMs. There's the infamous torque converter clutch on 3T40's but I had a bad tq converter o-ring on a Saturn TAAT do this. The torque converter has fluid going through it (duh) and on that particular transmission, low pressure caused lockup. The leak was minor enough that cold thick fluid still worked fine, and you see this a lot with o-rings and moving seals in transmissionmissions.

Valve bodies are easier surgery because they typically can be done with the transmission in the car, but I'd want some guarantee that doing it will actually fix your problem.

 

[lolford]

This is actually kind of common though I've seen it more on GMs. There's the infamous torque converter clutch on 3T40's but I had a bad tq converter o-ring on a Saturn TAAT do this. The torque converter has fluid going through it (duh) and on that particular transmission, low pressure caused lockup. The leak was minor enough that cold thick fluid still worked fine, and you see this a lot with o-rings and moving seals in transmissionmissions.

Valve bodies are easier surgery because they typically can be done with the transmission in the car, but I'd want some guarantee that doing it will actually fix your problem.

Short of doing a full rebuild I was given no guarantee sadly, part of me regrets not going with a used transmission since the scrapper would warranty it! Though the used transmission had the same miles as mine when the problem started. I think in GM land this is a 6T70?

Do you think it's worth replacing the solenoids too? I have the valvebody in hand already!

 

[Oillover]

I had a similar issue on an early 90s automatic Cavalier I once owned.
When exiting off the freeway, once the car came to a stop it would die.
It also started up with no issue.

The cause was sourced to the solenoid which locks the torque converter in the highest gear (to gain better fuel economy).
The stalling was similar to when you come to a stop with a manual transmission, but fail to depress the clutch or downshift.

Once the solenoid was unplugged, the problem disappeared with no noticeable difference to fuel consumption.

 

[K-Man]

When was the last time the fuel filter was changed? A clogged fuel filter alone might explain the symptoms.

 

[lolford]

I had this happen twice in my mkx with 3.7 but a little different .
Fully warmed up slowing down to stop ! would run as if missing service AWD warning would come on then stall it would restart and run fine. Cleaned throttle and so far hasn't returned in the last four months .

Thanks! New throttle body and MAF so that's out for me :/

I had a similar issue on an early 90s automatic Cavalier I once owned.
When exiting off the freeway, once the car came to a stop it would die.
It also started up with no issue.

The cause was sourced to the solenoid which locks the torque converter in the highest gear (to gain better fuel economy).
The stalling was similar to when you come to a stop with a manual transmission, but fail to depress the clutch or downshift.

Once the solenoid was unplugged, the problem disappeared with no noticeable difference to fuel consumption.

Thank you! Looks like I should probably replace the solenoids too!

When was the last time the fuel filter was changed? A clogged fuel filter alone might explain the symptoms.

Never, but the issue has been happening for a few years. No issues in any other scenario, so to change the filter I'd need to do the pump.

 

[The_Jeff]

Thank you! Looks like I should probably replace the solenoids too!

Whoa, pump the brakes-- your Ford is not necessarily anything like a 25-year old Cavalier.

Follow a diagnostic tree, at least so you can agree with your mechanic on the course of action.

 

[lolford]

Whoa, pump the brakes-- your Ford is not necessarily anything like a 25-year old Cavalier.

Follow a diagnostic tree, at least so you can agree with your mechanic on the course of action.

I didn't see anything in the ford repair manual. Even talking to the mechanic he said it's basically a crap shoot since there could be so many different causes.

The few shops I talked to before I had it serviced said it was probably the TC so everyone in my area is basically just guessing it seems!

 

[HemiBenny]

Sounds like the torque converter is possibly staying locked up. Throw it in neutral as you’re coming to a stop and see if it acts normal. Then leave it in drive the next time to see if it stumbles or stalls again.
I’ve seen this exact thing on several Subaru’s over the last few years.

 

[mk378]

Throw it in neutral as you’re coming to a stop and see if it acts normal.

Yes exactly. The test would be to shift to N before stopping. Then even if the converter is locked it won't stall. Though this also removes the normal load of idling in gear, so it may also cover up an airflow problem. Cleaning the throttle body and idle air valve (if it has one) is also something to try, a lot less expensive than tearing into the transmission.

 

[samven]

This may be a crap shoot but it does not cost anything to try. My 2012 Ford Fiesta was acting the same way but it would happen at stop lights every once in a while and only after it was at operating temp. It was a dirty throttle body. After cleaning it and running the re-calibration procedure (no computer needed) the problem went away and has stayed away for the last 3 years. It may not cure your issue but it costs 1 can of throttle body cleaner and about an hour of time.

 

[lolford]

Yes exactly. The test would be to shift to N before stopping. Then even if the converter is locked it won't stall. Though this also removes the normal load of idling in gear, so it may also cover up an airflow problem. Cleaning the throttle body and idle air valve (if it has one) is also something to try, a lot less expensive than tearing into the transmission.

Putting in neutral stops just fine, Though the mechanic and ford dealer said it doesn't mean much. I find if I give a bit of gas a few seconds before stopping (in drive) that usually is ok as well! TC has been replaced so wonder what else could it be?

When I check the scantool it's unlocked (or supposed to be) for a full 5+ seconds before I come to a stop. It doesn't seem to get "stuck" in lock at any other time though.

This may be a crap shoot but it does not cost anything to try. My 2012 Ford Fiesta was acting the same way but it would happen at stop lights every once in a while and only after it was at operating temp. It was a dirty throttle body. After cleaning it and running the re-calibration procedure (no computer needed) the problem went away and has stayed away for the last 3 years. It may not cure your issue but it costs 1 can of throttle body cleaner and about an hour of time.

I actually replaced both the MAF and throttle body (and reprogrammed) with no change :/

 

[RobbS]

I currently have a car that does same thing when I come to a stop at full temperature. It's heat related. Mine is a 5 speed manual.
Overheated relay comes to mind with my non-technical history.

 

[The_Jeff]

I'm beginning to think it's more of an engine tune-up/ throttle body issue. Also look for vacuum leaks. Also check your throttle position sensor voltages, TPSs go bad on Fords and they signal the PCM that your foot is off the gas so it's the computer's turn to control idle. With this faulty, the computer may just shrug and let itself stall.

The vacuum leak hypothesis holds water because the car runs richer when cold and with a higher idle, which masks small problems. What happens if you run the AC? Higher idle, fewer stalls?

If you didn't have a MAF I'd say take the intake tube off and cover the TB with your hand while it idles. It should fight to keep the idle speed through the idle speed control motor or electric throttle body. If it just sputters and dies without fighting you have ISC passages or motors to clean up.

With a MAF, it will probably still idle with the tube removed but hate you for it and it's not as high quality a test because it's already running in a compromised, fail-safe state.

 

[irad]

How old is the transmission fluid and filter? You can do a pan drop and change both if old or just replace the fluid. If the stalling decreases do another drain and fill. Check if the transmission shop used the correct fluid.

 

[lolford]

I'm beginning to think it's more of an engine tune-up/ throttle body issue. Also look for vacuum leaks. Also check your throttle position sensor voltages, TPSs go bad on Fords and they signal the PCM that your foot is off the gas so it's the computer's turn to control idle. With this faulty, the computer may just shrug and let itself stall.

The vacuum leak hypothesis holds water because the car runs richer when cold and with a higher idle, which masks small problems. What happens if you run the AC? Higher idle, fewer stalls?

If you didn't have a MAF I'd say take the intake tube off and cover the TB with your hand while it idles. It should fight to keep the idle speed through the idle speed control motor or electric throttle body. If it just sputters and dies without fighting you have ISC passages or motors to clean up.

With a MAF, it will probably still idle with the tube removed but hate you for it and it's not as high quality a test because it's already running in a compromised, fail-safe state.

I've had the same issue across two throttle bodies, the current one is brand new from the dealer and I did a relearn.

AC makes no difference, new MAF as well (again reset the KAM)

How old is the transmission fluid and filter? You can do a pan drop and change both if old or just replace the fluid. If the stalling decreases do another drain and fill.

Filter hasn't been changed but shop didn't suggest changing it during the TC change since it would've added $500 to the job. The transmission is on it's 3rd fluid change.

 

[irad]

My other thought is the egr valve. If you take it off clean the pipe going to the exhaust and the valve with carb cleaner.

 

[lolford]

My other thought is the egr valve. If you take it off clean the pipe going to the exhaust and the valve with carb cleaner.

No EGR valve in this engine afaik

 

[HemiBenny]

Putting in neutral stops just fine, Though the mechanic and ford dealer said it doesn't mean much. I find if I give a bit of gas a few seconds before stopping (in drive) that usually is ok as well! TC has been replaced so wonder what else could it be?

When I check the scantool it's unlocked (or supposed to be) for a full 5+ seconds before I come to a stop. It doesn't seem to get "stuck" in lock at any other time though.


I actually replaced both the MAF and throttle body (and reprogrammed) with no change :/

Just guessing, because that’s all we can do here, but I’m leaning towards the valve body. You said the shifting seemed to improve after the torque converter replacement. Did you experience rough or delayed shifting before?

It seems that you’ve covered most of the guesswork here. It needs to have someone get in it and actually diagnose the problem.
Best of luck to you.