I have an 04 F150 xlt with the 5.4l V8, it has a horrible idle and stalls. Dropping the rpms from 1 down to about 0 and jumping back up to almost 2 then back down until it stalls.
We have changed the battery, both camshaft position sensors, the rear fuel rail sensor, fuel filter, spark plugs, ignition coils. Still didn't solve the problem so we had it towed to a local Ford dealership and they ran the complete diagnostic test to check for anything including the smoke test for vacuum leaks, and their computer came back with the drivers side vct solenoid functioning at 0% and the passenger side at plus/minus 7° which they said with the driver side not working it would put the passenger side into retard mode. Towed the vehicle back home, changed both vct solenoids and the damn truck still runs the exact same. Should I call and see if they will rerun the test at no charge to see if maybe their computer was wrong? I don't know what else the issue could be, other than the pcm which I would think if that was bad I would be having more issues than just that. I am so lost, please help!!!

 

Have you tried reading the OBD codes? If so, please post them.

 

Yes, the only code that came back was PO340, that is the code that came up for the dealership as well.

 

Interesting...

I did a little digging and didn't quite find what I was hoping for. However, you can start reading here:

https://www.f150online.com/forums/20...e-problem.html

https://www.f150online.com/forums/v8...ped-p0340.html

https://www.youtube.com/watch?v=JPoN...ature=youtu.be

https://www.f150forum.com/f4/p0340-c...problem-33126/

 

I'm not sure man, we've literally tried everything besides the fuel pump and pcm. But when the dealership ran the diagnostic they told me their system would pin point the problem which came back as the vct solenoid on drivers side. We replaced both just so we could rule that out. I'm over $1000 into parts and labor already, just made my 3rd payment on the truck and purchased without the extended warranty because I couldn't afford it and now this happens. Maybe just bite the bullet and take it back to the dealership and tell them to call me when the truck is finished I can't waste more time and money into something that I don't know that's going to fix it. Thanks KS for your help

 

Well, the biggest problem is not understanding the code description.
Read it, it does say "circuit" error. It's not necessarily the sensor itself.
You can change the sensor a 100 times and other parts just hoping to get lucky and it won't fix a harness issue or plugup issue.
It's bank 1 the passenger side.
You dealer should have known this.
The computer is not getting the Sensor signal output it needs.
The computer needs to know how fast the cam is turning and where the cam is in Retard or Advance position. It's a VCT Crammed engine that moves cams' position.
The rolling idle is the system trying to gain control but can't due to the problem.
The code 340 tells it all.
Now you need some one who understands this and looks for the cause in the right area.
The trouble is not all that hard but takes labor time to chase it, then make the fix.
Good luck.

 

I had this problem. However it was only once the engine was hot. Did fuel filter, VCT selenoids, cleaned throttle body and problem was still there. Finally changed up viscosity of oil and added engine restore and it fixed my problem. I use 5w30 instead of 5w20 and the engine restore thickens it up a little bit also. Havent had my idle or stall problem since i changed this up. Hope this helps you.

 

random, what you did was not a Fix but a cover up of the issue.
It will come back.
Good luck.

 

Yeah, so you think phasers?

 

Yes because they are oil viscosity sensitive.
Designed for operation with original spec oil weight.
If an increase in viscosity makes a difference, it shows they are worn and will fault again later.
I don't think you would go to 40 or 50 weight oil later just to keep them working.
Good luck.

 

Thats what I figured. I actually plan to replace them this spring. In the mean time, thcker oil is holding up.

 

Vehicle was taken to the dealership, it was unknown to me that I had an extended warranty, must have missed that part of the conversation. They said they had to rip valve pan covers off and do a compression test on oil pressure, and check for any sludge in the engine. If vehicle had faults with either of those then the warranty company would not consider this a warranty claim, which doesn't make sense to me considering I just purchased 3 months ago. Anyways, everything came back fine, my cam phasers went bad which made the timing chain skip a few teeth, and ruined a few parts. Everything is under warranty and I pay $100 deductible for a $2700+ job, I'll take it!! Thanks for all of your advice!

 

Good deal!! Glad to see a warranty get used.

If it's a Ford warranty -- you might be able to extend it again. I'd inquire to see the cost.