2007 F150 Lariat Crew 4x4 - 5.4L V8 Triton V3
Miles: 179,600



What is the issue?
When at idle, engine is fine on a cold start. When driving the engine shifts and runs smooth. Once the engine is at “Normal Operating Temperature” under idle after braking while in Drive or Reverse (load), the engine will begin to run rough, leading to a stall. If you feather the gas pedal, it will keep it from stalling. Repeat issue until engine is shut off. If the engine does stall if you do not feather it, you can restart the engine, however, it is a hard turn over and start. Then once restarted, engine is smooth running, but it begins to repeat the described above.

Engine Codes:
No codes thrown unfortunately either.



What I’ve done/had done:
New - Spark Plugs
New - Coil Packs as needed
New - Throttle Position Sensor
New - Catalytic Convertors (both)
New - Fuel Pump Driver Module
Cleaned - Throttle Body Plate (buttery-fly), inspected and springs to return position nicely
Looked at the Throttle Body Motor, looked clean (did not do anything with it but put back together)
Cleaned - Mass Air Flow Sensor
Looked for Vacuum leaks, unable to find any

Conducted PCM reprogramming after 30 Minutes of complete power drain and disconnection of battery. Conducted throttle position programming after the new Throttle Position Sensor was installed. Conducted PCM reprogramming again after TPS programming after 8 – 10 HRS (overnight) of complete power drain and disconnection of battery by using the following steps:

1. Turn the key to the on position (engine off)
2. Slowly depress the gas pedal all the way to the floor.
3. Quickly release the gas pedal, so that it come back up on its own.
4. Turn the key to the off position and repeat the cycle 3 times.
5. Turn the engine on.

Did the Idle Relearn:
Put gear shifter in "P" (Park), turn off all accessories. Run the engine until it reaches normal operating temperature. Allow engine to idle for at least one minute. Turn the air conditioning on and allow the engine to idle for at least one minute.

Could the throttle body motor be bad? Any other ideas?

Thanks in advance for any help!

 

Sounds to me like maybe a vct /phaser issue. These show up more when the engine is warmed up and the oil thins out at operating temp.
what weight of oil are you running. I would use 5w30 instead of 5w20.
I think you can test this theory by unplugging the vct solenoids when at temp and see if this keeps it from stalling.

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Thank you for your feedback. I am going to do this test tonight and report back. I assume I should be able to drive the vehicle for the test?

 

Yes you can drive it. As mentioned in the video it will make the check engine light come on, but should do no harm to take it for a test drive this way.

 

Oh! I thought the video was an ad - my fault. I will give it a shot.

 

Probably in need of replacing the phasers at a minimum. More than likely though, a timing job.

 

Report: Drove the truck and the engine got to normal operating temperature. Had the stall happen as expected. Shut down truck, did not try to restart. Popped the hood (had the socket to loosen and move the drivers side fluid reservoir with me) and unplugged both of the VCT's; it was a 3 minute job to unplug the VCT's so the engine hadn't time to cool down. Started truck, ran good. Drove around town for another 45 minutes, stop signs, lights, everywhere I could stop with it under load and it just idled normally. I think there is something with the VCTs as needsmoarturbo had indicated. I now have a plan of attack and a starting point. I am grateful for everyone's insight on this and help in the direction to look! At least all the other things are replaced, cleaned and inspected!

 

Glad to hear you have narrowed it down. I'm not sure what the fix is though.
I think if it were me I'd start with the vct solenoid/s and see if that takes care of it. You have an 07 so if it's an early one I think you can still replace the solenoids without removing the valve covers. Later in 07 there was a change and those require the valve cover to be removed first to get the solenoids out.
These motors suffer all kinds of issues if the oil pressure isn't good enough, so if you aren't running 5w30 already I'd switch to that and see if you get any improvement.
If none of the above resolve the issue long term you may need to update the timing components and oil pump to a high volume one.
Start with the easy things first though, like thicker oil and vct solenoids.